[WebKit-https.git] / Source / WebCore / rendering / RenderBlock.cpp

/*
 * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
 *           (C) 1999 Antti Koivisto (koivisto@kde.org)
 *           (C) 2007 David Smith (catfish.man@gmail.com)
 * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
 * Copyright (C) Research In Motion Limited 2010. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include "config.h"
#include "RenderBlock.h"

#include "ColumnInfo.h"
#include "Document.h"
#include "Element.h"
#include "FloatQuad.h"
#include "Frame.h"
#include "FrameSelection.h"
#include "FrameView.h"
#include "GraphicsContext.h"
#include "HTMLFormElement.h"
#include "HTMLNames.h"
#include "HitTestResult.h"
#include "InlineIterator.h"
#include "InlineTextBox.h"
#include "LayoutRepainter.h"
#include "Page.h"
#include "PaintInfo.h"
#include "RenderBoxRegionInfo.h"
#include "RenderCombineText.h"
#include "RenderDeprecatedFlexibleBox.h"
#include "RenderFlowThread.h"
#include "RenderImage.h"
#include "RenderInline.h"
#include "RenderLayer.h"
#include "RenderMarquee.h"
#include "RenderRegion.h"
#include "RenderReplica.h"
#include "RenderTableCell.h"
#include "RenderTextFragment.h"
#include "RenderTheme.h"
#include "RenderView.h"
#include "Settings.h"
#include "SVGTextRunRenderingContext.h"
#include "TransformState.h"
#include <wtf/StdLibExtras.h>

using namespace std;
using namespace WTF;
using namespace Unicode;

namespace WebCore {

using namespace HTMLNames;

typedef WTF::HashMap<const RenderBox*, ColumnInfo*> ColumnInfoMap;
static ColumnInfoMap* gColumnInfoMap = 0;

typedef WTF::HashMap<const RenderBlock*, HashSet<RenderBox*>*> PercentHeightDescendantsMap;
static PercentHeightDescendantsMap* gPercentHeightDescendantsMap = 0;

typedef WTF::HashMap<const RenderBox*, HashSet<RenderBlock*>*> PercentHeightContainerMap;
static PercentHeightContainerMap* gPercentHeightContainerMap = 0;
    
typedef WTF::HashMap<RenderBlock*, ListHashSet<RenderInline*>*> ContinuationOutlineTableMap;

typedef WTF::HashSet<RenderBlock*> DelayedUpdateScrollInfoSet;
static int gDelayUpdateScrollInfo = 0;
static DelayedUpdateScrollInfoSet* gDelayedUpdateScrollInfoSet = 0;

bool RenderBlock::s_canPropagateFloatIntoSibling = false;

// Our MarginInfo state used when laying out block children.
RenderBlock::MarginInfo::MarginInfo(RenderBlock* block, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding)
    : m_atBeforeSideOfBlock(true)
    , m_atAfterSideOfBlock(false)
    , m_marginBeforeQuirk(false)
    , m_marginAfterQuirk(false)
    , m_determinedMarginBeforeQuirk(false)
{
    // Whether or not we can collapse our own margins with our children.  We don't do this
    // if we had any border/padding (obviously), if we're the root or HTML elements, or if
    // we're positioned, floating, a table cell.
    m_canCollapseWithChildren = !block->isRenderView() && !block->isRoot() && !block->isPositioned()
        && !block->isFloating() && !block->isTableCell() && !block->hasOverflowClip() && !block->isInlineBlockOrInlineTable()
        && !block->isWritingModeRoot() && block->style()->hasAutoColumnCount() && block->style()->hasAutoColumnWidth()
        && !block->style()->columnSpan();

    m_canCollapseMarginBeforeWithChildren = m_canCollapseWithChildren && (beforeBorderPadding == 0) && block->style()->marginBeforeCollapse() != MSEPARATE;

    // If any height other than auto is specified in CSS, then we don't collapse our bottom
    // margins with our children's margins.  To do otherwise would be to risk odd visual
    // effects when the children overflow out of the parent block and yet still collapse
    // with it.  We also don't collapse if we have any bottom border/padding.
    m_canCollapseMarginAfterWithChildren = m_canCollapseWithChildren && (afterBorderPadding == 0) &&
        (block->style()->logicalHeight().isAuto() && block->style()->logicalHeight().value() == 0) && block->style()->marginAfterCollapse() != MSEPARATE;
    
    m_quirkContainer = block->isTableCell() || block->isBody() || block->style()->marginBeforeCollapse() == MDISCARD || 
        block->style()->marginAfterCollapse() == MDISCARD;

    m_positiveMargin = m_canCollapseMarginBeforeWithChildren ? block->maxPositiveMarginBefore() : 0;
    m_negativeMargin = m_canCollapseMarginBeforeWithChildren ? block->maxNegativeMarginBefore() : 0;
}

// -------------------------------------------------------------------------------------------------------

RenderBlock::RenderBlock(Node* node)
      : RenderBox(node)
      , m_lineHeight(-1)
      , m_beingDestroyed(false)
      , m_hasPositionedFloats(false)
{
    setChildrenInline(true);
}

RenderBlock::~RenderBlock()
{
    if (m_floatingObjects)
        deleteAllValues(m_floatingObjects->set());
    
    if (hasColumns())
        delete gColumnInfoMap->take(this);

    if (gPercentHeightDescendantsMap) {
        if (HashSet<RenderBox*>* descendantSet = gPercentHeightDescendantsMap->take(this)) {
            HashSet<RenderBox*>::iterator end = descendantSet->end();
            for (HashSet<RenderBox*>::iterator descendant = descendantSet->begin(); descendant != end; ++descendant) {
                HashSet<RenderBlock*>* containerSet = gPercentHeightContainerMap->get(*descendant);
                ASSERT(containerSet);
                if (!containerSet)
                    continue;
                ASSERT(containerSet->contains(this));
                containerSet->remove(this);
                if (containerSet->isEmpty()) {
                    gPercentHeightContainerMap->remove(*descendant);
                    delete containerSet;
                }
            }
            delete descendantSet;
        }
    }
}

void RenderBlock::willBeDestroyed()
{
    // Mark as being destroyed to avoid trouble with merges in removeChild().
    m_beingDestroyed = true;

    // Make sure to destroy anonymous children first while they are still connected to the rest of the tree, so that they will
    // properly dirty line boxes that they are removed from. Effects that do :before/:after only on hover could crash otherwise.
    children()->destroyLeftoverChildren();

    // Destroy our continuation before anything other than anonymous children.
    // The reason we don't destroy it before anonymous children is that they may
    // have continuations of their own that are anonymous children of our continuation.
    RenderBoxModelObject* continuation = this->continuation();
    if (continuation) {
        continuation->destroy();
        setContinuation(0);
    }
    
    if (!documentBeingDestroyed()) {
        if (firstLineBox()) {
            // We can't wait for RenderBox::destroy to clear the selection,
            // because by then we will have nuked the line boxes.
            // FIXME: The FrameSelection should be responsible for this when it
            // is notified of DOM mutations.
            if (isSelectionBorder())
                view()->clearSelection();

            // If we are an anonymous block, then our line boxes might have children
            // that will outlast this block. In the non-anonymous block case those
            // children will be destroyed by the time we return from this function.
            if (isAnonymousBlock()) {
                for (InlineFlowBox* box = firstLineBox(); box; box = box->nextLineBox()) {
                    while (InlineBox* childBox = box->firstChild())
                        childBox->remove();
                }
            }
        } else if (parent())
            parent()->dirtyLinesFromChangedChild(this);
    }

    m_lineBoxes.deleteLineBoxes(renderArena());

    if (UNLIKELY(gDelayedUpdateScrollInfoSet != 0))
        gDelayedUpdateScrollInfoSet->remove(this);

    RenderBox::willBeDestroyed();
}

void RenderBlock::styleWillChange(StyleDifference diff, const RenderStyle* newStyle)
{
    s_canPropagateFloatIntoSibling = style() ? !isFloatingOrPositioned() && !avoidsFloats() : false;

    setReplaced(newStyle->isDisplayInlineType());
    
    if (style() && parent() && diff == StyleDifferenceLayout && style()->position() != newStyle->position()) {
        if (newStyle->position() == StaticPosition)
            // Clear our positioned objects list. Our absolutely positioned descendants will be
            // inserted into our containing block's positioned objects list during layout.
            removePositionedObjects(0);
        else if (style()->position() == StaticPosition) {
            // Remove our absolutely positioned descendants from their current containing block.
            // They will be inserted into our positioned objects list during layout.
            RenderObject* cb = parent();
            while (cb && (cb->style()->position() == StaticPosition || (cb->isInline() && !cb->isReplaced())) && !cb->isRenderView()) {
                if (cb->style()->position() == RelativePosition && cb->isInline() && !cb->isReplaced()) {
                    cb = cb->containingBlock();
                    break;
                }
                cb = cb->parent();
            }
            
            if (cb->isRenderBlock())
                toRenderBlock(cb)->removePositionedObjects(this);
        }

        if (containsFloats() && !isFloating() && !isPositioned() && (newStyle->position() == AbsolutePosition || newStyle->position() == FixedPosition))
            markAllDescendantsWithFloatsForLayout();
    }

    RenderBox::styleWillChange(diff, newStyle);
}

void RenderBlock::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
{
    RenderBox::styleDidChange(diff, oldStyle);

    if (!isAnonymousBlock()) {
        // Ensure that all of our continuation blocks pick up the new style.
        for (RenderBlock* currCont = blockElementContinuation(); currCont; currCont = currCont->blockElementContinuation()) {
            RenderBoxModelObject* nextCont = currCont->continuation();
            currCont->setContinuation(0);
            currCont->setStyle(style());
            currCont->setContinuation(nextCont);
        }
    }

    propagateStyleToAnonymousChildren(true);    
    m_lineHeight = -1;

    // Update pseudos for :before and :after now.
    if (!isAnonymous() && document()->usesBeforeAfterRules() && canHaveChildren()) {
        updateBeforeAfterContent(BEFORE);
        updateBeforeAfterContent(AFTER);
    }

    // After our style changed, if we lose our ability to propagate floats into next sibling
    // blocks, then we need to find the top most parent containing that overhanging float and
    // then mark its descendants with floats for layout and clear all floats from its next
    // sibling blocks that exist in our floating objects list. See bug 56299 and 62875.
    bool canPropagateFloatIntoSibling = !isFloatingOrPositioned() && !avoidsFloats();
    if (diff == StyleDifferenceLayout && s_canPropagateFloatIntoSibling && !canPropagateFloatIntoSibling && hasOverhangingFloats()) {
        RenderBlock* parentBlock = this;
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator end = floatingObjectSet.end();

        for (RenderObject* curr = parent(); curr && !curr->isRenderView(); curr = curr->parent()) {
            if (curr->isRenderBlock()) {
                RenderBlock* currBlock = toRenderBlock(curr);

                if (currBlock->hasOverhangingFloats()) {
                    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                        RenderBox* renderer = (*it)->renderer();
                        if (currBlock->hasOverhangingFloat(renderer)) {
                            parentBlock = currBlock;
                            break;
                        }
                    }
                }
            }
        }
              
        parentBlock->markAllDescendantsWithFloatsForLayout();
        parentBlock->markSiblingsWithFloatsForLayout();
    }
}

void RenderBlock::updateBeforeAfterContent(PseudoId pseudoId)
{
    // If this is an anonymous wrapper, then the parent applies its own pseudo-element style to it.
    if (parent() && parent()->createsAnonymousWrapper())
        return;
    return children()->updateBeforeAfterContent(this, pseudoId);
}

RenderBlock* RenderBlock::continuationBefore(RenderObject* beforeChild)
{
    if (beforeChild && beforeChild->parent() == this)
        return this;

    RenderBlock* curr = toRenderBlock(continuation());
    RenderBlock* nextToLast = this;
    RenderBlock* last = this;
    while (curr) {
        if (beforeChild && beforeChild->parent() == curr) {
            if (curr->firstChild() == beforeChild)
                return last;
            return curr;
        }

        nextToLast = last;
        last = curr;
        curr = toRenderBlock(curr->continuation());
    }

    if (!beforeChild && !last->firstChild())
        return nextToLast;
    return last;
}

void RenderBlock::addChildToContinuation(RenderObject* newChild, RenderObject* beforeChild)
{
    RenderBlock* flow = continuationBefore(beforeChild);
    ASSERT(!beforeChild || beforeChild->parent()->isAnonymousColumnSpanBlock() || beforeChild->parent()->isRenderBlock());
    RenderBoxModelObject* beforeChildParent = 0;
    if (beforeChild)
        beforeChildParent = toRenderBoxModelObject(beforeChild->parent());
    else {
        RenderBoxModelObject* cont = flow->continuation();
        if (cont)
            beforeChildParent = cont;
        else
            beforeChildParent = flow;
    }

    if (newChild->isFloatingOrPositioned())
        return beforeChildParent->addChildIgnoringContinuation(newChild, beforeChild);

    // A continuation always consists of two potential candidates: a block or an anonymous
    // column span box holding column span children.
    bool childIsNormal = newChild->isInline() || !newChild->style()->columnSpan();
    bool bcpIsNormal = beforeChildParent->isInline() || !beforeChildParent->style()->columnSpan();
    bool flowIsNormal = flow->isInline() || !flow->style()->columnSpan();

    if (flow == beforeChildParent)
        return flow->addChildIgnoringContinuation(newChild, beforeChild);
    
    // The goal here is to match up if we can, so that we can coalesce and create the
    // minimal # of continuations needed for the inline.
    if (childIsNormal == bcpIsNormal)
        return beforeChildParent->addChildIgnoringContinuation(newChild, beforeChild);
    if (flowIsNormal == childIsNormal)
        return flow->addChildIgnoringContinuation(newChild, 0); // Just treat like an append.
    return beforeChildParent->addChildIgnoringContinuation(newChild, beforeChild);
}


void RenderBlock::addChildToAnonymousColumnBlocks(RenderObject* newChild, RenderObject* beforeChild)
{
    ASSERT(!continuation()); // We don't yet support column spans that aren't immediate children of the multi-column block.
        
    // The goal is to locate a suitable box in which to place our child.
    RenderBlock* beforeChildParent = toRenderBlock(beforeChild && beforeChild->parent()->isRenderBlock() ? beforeChild->parent() : lastChild());
    
    // If the new child is floating or positioned it can just go in that block.
    if (newChild->isFloatingOrPositioned())
        return beforeChildParent->addChildIgnoringAnonymousColumnBlocks(newChild, beforeChild);

    // See if the child can be placed in the box.
    bool newChildHasColumnSpan = newChild->style()->columnSpan() && !newChild->isInline();
    bool beforeChildParentHoldsColumnSpans = beforeChildParent->isAnonymousColumnSpanBlock();

    if (newChildHasColumnSpan == beforeChildParentHoldsColumnSpans)
        return beforeChildParent->addChildIgnoringAnonymousColumnBlocks(newChild, beforeChild);

    if (!beforeChild) {
        // Create a new block of the correct type.
        RenderBlock* newBox = newChildHasColumnSpan ? createAnonymousColumnSpanBlock() : createAnonymousColumnsBlock();
        children()->appendChildNode(this, newBox);
        newBox->addChildIgnoringAnonymousColumnBlocks(newChild, 0);
        return;
    }

    RenderObject* immediateChild = beforeChild;
    bool isPreviousBlockViable = true;
    while (immediateChild->parent() != this) {
        if (isPreviousBlockViable)
            isPreviousBlockViable = !immediateChild->previousSibling();
        immediateChild = immediateChild->parent();
    }
    if (isPreviousBlockViable && immediateChild->previousSibling())
        return toRenderBlock(immediateChild->previousSibling())->addChildIgnoringAnonymousColumnBlocks(newChild, 0); // Treat like an append.
        
    // Split our anonymous blocks.
    RenderObject* newBeforeChild = splitAnonymousBlocksAroundChild(beforeChild);
    
    // Create a new anonymous box of the appropriate type.
    RenderBlock* newBox = newChildHasColumnSpan ? createAnonymousColumnSpanBlock() : createAnonymousColumnsBlock();
    children()->insertChildNode(this, newBox, newBeforeChild);
    newBox->addChildIgnoringAnonymousColumnBlocks(newChild, 0);
    return;
}

RenderBlock* RenderBlock::containingColumnsBlock(bool allowAnonymousColumnBlock)
{
    for (RenderObject* curr = this; curr; curr = curr->parent()) {
        if (!curr->isRenderBlock() || curr->isFloatingOrPositioned() || curr->isTableCell() || curr->isRoot() || curr->isRenderView() || curr->hasOverflowClip()
            || curr->isInlineBlockOrInlineTable())
            return 0;
        
        RenderBlock* currBlock = toRenderBlock(curr);
        if (currBlock->style()->specifiesColumns() && (allowAnonymousColumnBlock || !currBlock->isAnonymousColumnsBlock()))
            return currBlock;
            
        if (currBlock->isAnonymousColumnSpanBlock())
            return 0;
    }
    return 0;
}

RenderBlock* RenderBlock::clone() const
{
    RenderBlock* cloneBlock;
    if (isAnonymousBlock())
        cloneBlock = createAnonymousBlock();
    else {
        cloneBlock = new (renderArena()) RenderBlock(node());
        cloneBlock->setStyle(style());
    }
    cloneBlock->setChildrenInline(childrenInline());
    return cloneBlock;
}

void RenderBlock::splitBlocks(RenderBlock* fromBlock, RenderBlock* toBlock,
                              RenderBlock* middleBlock,
                              RenderObject* beforeChild, RenderBoxModelObject* oldCont)
{
    // Create a clone of this inline.
    RenderBlock* cloneBlock = clone();
    if (!isAnonymousBlock())
        cloneBlock->setContinuation(oldCont);

    // Now take all of the children from beforeChild to the end and remove
    // them from |this| and place them in the clone.
    if (!beforeChild && isAfterContent(lastChild()))
        beforeChild = lastChild();
    moveChildrenTo(cloneBlock, beforeChild, 0);
    
    // Hook |clone| up as the continuation of the middle block.
    if (!cloneBlock->isAnonymousBlock())
        middleBlock->setContinuation(cloneBlock);

    // We have been reparented and are now under the fromBlock.  We need
    // to walk up our block parent chain until we hit the containing anonymous columns block.
    // Once we hit the anonymous columns block we're done.
    RenderBoxModelObject* curr = toRenderBoxModelObject(parent());
    RenderBoxModelObject* currChild = this;
    
    while (curr && curr != fromBlock) {
        ASSERT(curr->isRenderBlock());
        
        RenderBlock* blockCurr = toRenderBlock(curr);
        
        // Create a new clone.
        RenderBlock* cloneChild = cloneBlock;
        cloneBlock = blockCurr->clone();

        // Insert our child clone as the first child.
        cloneBlock->children()->appendChildNode(cloneBlock, cloneChild);

        // Hook the clone up as a continuation of |curr|.  Note we do encounter
        // anonymous blocks possibly as we walk up the block chain.  When we split an
        // anonymous block, there's no need to do any continuation hookup, since we haven't
        // actually split a real element.
        if (!blockCurr->isAnonymousBlock()) {
            oldCont = blockCurr->continuation();
            blockCurr->setContinuation(cloneBlock);
            cloneBlock->setContinuation(oldCont);
        }

        // Someone may have indirectly caused a <q> to split.  When this happens, the :after content
        // has to move into the inline continuation.  Call updateBeforeAfterContent to ensure that the inline's :after
        // content gets properly destroyed.
        if (document()->usesBeforeAfterRules())
            blockCurr->children()->updateBeforeAfterContent(blockCurr, AFTER);

        // Now we need to take all of the children starting from the first child
        // *after* currChild and append them all to the clone.
        RenderObject* afterContent = isAfterContent(cloneBlock->lastChild()) ? cloneBlock->lastChild() : 0;
        blockCurr->moveChildrenTo(cloneBlock, currChild->nextSibling(), 0, afterContent);

        // Keep walking up the chain.
        currChild = curr;
        curr = toRenderBoxModelObject(curr->parent());
    }

    // Now we are at the columns block level. We need to put the clone into the toBlock.
    toBlock->children()->appendChildNode(toBlock, cloneBlock);

    // Now take all the children after currChild and remove them from the fromBlock
    // and put them in the toBlock.
    fromBlock->moveChildrenTo(toBlock, currChild->nextSibling(), 0);
}

void RenderBlock::splitFlow(RenderObject* beforeChild, RenderBlock* newBlockBox,
                            RenderObject* newChild, RenderBoxModelObject* oldCont)
{
    RenderBlock* pre = 0;
    RenderBlock* block = containingColumnsBlock();
    
    // Delete our line boxes before we do the inline split into continuations.
    block->deleteLineBoxTree();
    
    bool madeNewBeforeBlock = false;
    if (block->isAnonymousColumnsBlock()) {
        // We can reuse this block and make it the preBlock of the next continuation.
        pre = block;
        pre->removePositionedObjects(0);
        block = toRenderBlock(block->parent());
    } else {
        // No anonymous block available for use.  Make one.
        pre = block->createAnonymousColumnsBlock();
        pre->setChildrenInline(false);
        madeNewBeforeBlock = true;
    }

    RenderBlock* post = block->createAnonymousColumnsBlock();
    post->setChildrenInline(false);

    RenderObject* boxFirst = madeNewBeforeBlock ? block->firstChild() : pre->nextSibling();
    if (madeNewBeforeBlock)
        block->children()->insertChildNode(block, pre, boxFirst);
    block->children()->insertChildNode(block, newBlockBox, boxFirst);
    block->children()->insertChildNode(block, post, boxFirst);
    block->setChildrenInline(false);
    
    if (madeNewBeforeBlock)
        block->moveChildrenTo(pre, boxFirst, 0);

    splitBlocks(pre, post, newBlockBox, beforeChild, oldCont);

    // We already know the newBlockBox isn't going to contain inline kids, so avoid wasting
    // time in makeChildrenNonInline by just setting this explicitly up front.
    newBlockBox->setChildrenInline(false);

    // We delayed adding the newChild until now so that the |newBlockBox| would be fully
    // connected, thus allowing newChild access to a renderArena should it need
    // to wrap itself in additional boxes (e.g., table construction).
    newBlockBox->addChild(newChild);

    // Always just do a full layout in order to ensure that line boxes (especially wrappers for images)
    // get deleted properly.  Because objects moves from the pre block into the post block, we want to
    // make new line boxes instead of leaving the old line boxes around.
    pre->setNeedsLayoutAndPrefWidthsRecalc();
    block->setNeedsLayoutAndPrefWidthsRecalc();
    post->setNeedsLayoutAndPrefWidthsRecalc();
}

RenderObject* RenderBlock::splitAnonymousBlocksAroundChild(RenderObject* beforeChild)
{
    while (beforeChild->parent() != this) {
        RenderBlock* blockToSplit = toRenderBlock(beforeChild->parent());
        if (blockToSplit->firstChild() != beforeChild) {
            // We have to split the parentBlock into two blocks.
            RenderBlock* post = createAnonymousBlockWithSameTypeAs(blockToSplit);
            post->setChildrenInline(blockToSplit->childrenInline());
            RenderBlock* parentBlock = toRenderBlock(blockToSplit->parent());
            parentBlock->children()->insertChildNode(parentBlock, post, blockToSplit->nextSibling());
            blockToSplit->moveChildrenTo(post, beforeChild, 0, blockToSplit->hasLayer());
            post->setNeedsLayoutAndPrefWidthsRecalc();
            blockToSplit->setNeedsLayoutAndPrefWidthsRecalc();
            beforeChild = post;
        } else
            beforeChild = blockToSplit;
    }
    return beforeChild;
}

void RenderBlock::makeChildrenAnonymousColumnBlocks(RenderObject* beforeChild, RenderBlock* newBlockBox, RenderObject* newChild)
{
    RenderBlock* pre = 0;
    RenderBlock* post = 0;
    RenderBlock* block = this; // Eventually block will not just be |this|, but will also be a block nested inside |this|.  Assign to a variable
                               // so that we don't have to patch all of the rest of the code later on.
    
    // Delete the block's line boxes before we do the split.
    block->deleteLineBoxTree();

    if (beforeChild && beforeChild->parent() != this)
        beforeChild = splitAnonymousBlocksAroundChild(beforeChild);

    if (beforeChild != firstChild()) {
        pre = block->createAnonymousColumnsBlock();
        pre->setChildrenInline(block->childrenInline());
    }

    if (beforeChild) {
        post = block->createAnonymousColumnsBlock();
        post->setChildrenInline(block->childrenInline());
    }

    RenderObject* boxFirst = block->firstChild();
    if (pre)
        block->children()->insertChildNode(block, pre, boxFirst);
    block->children()->insertChildNode(block, newBlockBox, boxFirst);
    if (post)
        block->children()->insertChildNode(block, post, boxFirst);
    block->setChildrenInline(false);
    
    // The pre/post blocks always have layers, so we know to always do a full insert/remove (so we pass true as the last argument).
    block->moveChildrenTo(pre, boxFirst, beforeChild, true);
    block->moveChildrenTo(post, beforeChild, 0, true);

    // We already know the newBlockBox isn't going to contain inline kids, so avoid wasting
    // time in makeChildrenNonInline by just setting this explicitly up front.
    newBlockBox->setChildrenInline(false);

    // We delayed adding the newChild until now so that the |newBlockBox| would be fully
    // connected, thus allowing newChild access to a renderArena should it need
    // to wrap itself in additional boxes (e.g., table construction).
    newBlockBox->addChild(newChild);

    // Always just do a full layout in order to ensure that line boxes (especially wrappers for images)
    // get deleted properly.  Because objects moved from the pre block into the post block, we want to
    // make new line boxes instead of leaving the old line boxes around.
    if (pre)
        pre->setNeedsLayoutAndPrefWidthsRecalc();
    block->setNeedsLayoutAndPrefWidthsRecalc();
    if (post)
        post->setNeedsLayoutAndPrefWidthsRecalc();
}

RenderBlock* RenderBlock::columnsBlockForSpanningElement(RenderObject* newChild)
{
    // FIXME: This function is the gateway for the addition of column-span support.  It will
    // be added to in three stages:
    // (1) Immediate children of a multi-column block can span.
    // (2) Nested block-level children with only block-level ancestors between them and the multi-column block can span.
    // (3) Nested children with block or inline ancestors between them and the multi-column block can span (this is when we
    // cross the streams and have to cope with both types of continuations mixed together).
    // This function currently supports (1) and (2).
    RenderBlock* columnsBlockAncestor = 0;
    if (!newChild->isText() && newChild->style()->columnSpan() && !newChild->isFloatingOrPositioned()
        && !newChild->isInline() && !isAnonymousColumnSpanBlock()) {
        if (style()->specifiesColumns())
            columnsBlockAncestor = this;
        else if (!isInline() && parent() && parent()->isRenderBlock()) {
            columnsBlockAncestor = toRenderBlock(parent())->containingColumnsBlock(false);
            
            if (columnsBlockAncestor) {
                // Make sure that none of the parent ancestors have a continuation.
                // If yes, we do not want split the block into continuations.
                RenderObject* curr = this;
                while (curr && curr != columnsBlockAncestor) {
                    if (curr->isRenderBlock() && toRenderBlock(curr)->continuation()) {
                        columnsBlockAncestor = 0;
                        break;
                    }
                    curr = curr->parent();
                }
            }
        }
    }
    return columnsBlockAncestor;
}

void RenderBlock::addChildIgnoringAnonymousColumnBlocks(RenderObject* newChild, RenderObject* beforeChild)
{
    // Make sure we don't append things after :after-generated content if we have it.
    if (!beforeChild)
        beforeChild = findAfterContentRenderer();

    // If the requested beforeChild is not one of our children, then this is because
    // there is an anonymous container within this object that contains the beforeChild.
    if (beforeChild && beforeChild->parent() != this) {
        RenderObject* beforeChildAnonymousContainer = anonymousContainer(beforeChild);
        ASSERT(beforeChildAnonymousContainer);
        ASSERT(beforeChildAnonymousContainer->isAnonymous());

        if (beforeChildAnonymousContainer->isAnonymousBlock()) {
            // Insert the child into the anonymous block box instead of here.
            if (newChild->isInline() || beforeChild->parent()->firstChild() != beforeChild)
                beforeChild->parent()->addChild(newChild, beforeChild);
            else
                addChild(newChild, beforeChild->parent());
            return;
        }

        ASSERT(beforeChildAnonymousContainer->isTable());
        if ((newChild->isTableCol() && newChild->style()->display() == TABLE_COLUMN_GROUP)
                || (newChild->isRenderBlock() && newChild->style()->display() == TABLE_CAPTION)
                || newChild->isTableSection()
                || newChild->isTableRow()
                || newChild->isTableCell()) {
            // Insert into the anonymous table.
            beforeChildAnonymousContainer->addChild(newChild, beforeChild);
            return;
        }

        // Go on to insert before the anonymous table.
        beforeChild = beforeChildAnonymousContainer;
    }

    // Check for a spanning element in columns.
    RenderBlock* columnsBlockAncestor = columnsBlockForSpanningElement(newChild);
    if (columnsBlockAncestor) {
        // We are placing a column-span element inside a block. 
        RenderBlock* newBox = createAnonymousColumnSpanBlock();
        
        if (columnsBlockAncestor != this) {
            // We are nested inside a multi-column element and are being split by the span.  We have to break up
            // our block into continuations.
            RenderBoxModelObject* oldContinuation = continuation();
            setContinuation(newBox);

            // Someone may have put a <p> inside a <q>, causing a split.  When this happens, the :after content
            // has to move into the inline continuation.  Call updateBeforeAfterContent to ensure that our :after
            // content gets properly destroyed.
            bool isLastChild = (beforeChild == lastChild());
            if (document()->usesBeforeAfterRules())
                children()->updateBeforeAfterContent(this, AFTER);
            if (isLastChild && beforeChild != lastChild())
                beforeChild = 0; // We destroyed the last child, so now we need to update our insertion
                                 // point to be 0.  It's just a straight append now.

            splitFlow(beforeChild, newBox, newChild, oldContinuation);
            return;
        }

        // We have to perform a split of this block's children.  This involves creating an anonymous block box to hold
        // the column-spanning |newChild|.  We take all of the children from before |newChild| and put them into
        // one anonymous columns block, and all of the children after |newChild| go into another anonymous block.
        makeChildrenAnonymousColumnBlocks(beforeChild, newBox, newChild);
        return;
    }

    bool madeBoxesNonInline = false;

    // A block has to either have all of its children inline, or all of its children as blocks.
    // So, if our children are currently inline and a block child has to be inserted, we move all our
    // inline children into anonymous block boxes.
    if (childrenInline() && !newChild->isInline() && !newChild->isFloatingOrPositioned()) {
        // This is a block with inline content. Wrap the inline content in anonymous blocks.
        makeChildrenNonInline(beforeChild);
        madeBoxesNonInline = true;

        if (beforeChild && beforeChild->parent() != this) {
            beforeChild = beforeChild->parent();
            ASSERT(beforeChild->isAnonymousBlock());
            ASSERT(beforeChild->parent() == this);
        }
    } else if (!childrenInline() && (newChild->isFloatingOrPositioned() || newChild->isInline())) {
        // If we're inserting an inline child but all of our children are blocks, then we have to make sure
        // it is put into an anomyous block box. We try to use an existing anonymous box if possible, otherwise
        // a new one is created and inserted into our list of children in the appropriate position.
        RenderObject* afterChild = beforeChild ? beforeChild->previousSibling() : lastChild();

        if (afterChild && afterChild->isAnonymousBlock()) {
            afterChild->addChild(newChild);
            return;
        }

        if (newChild->isInline()) {
            // No suitable existing anonymous box - create a new one.
            RenderBlock* newBox = createAnonymousBlock();
            RenderBox::addChild(newBox, beforeChild);
            newBox->addChild(newChild);
            return;
        }
    }

    RenderBox::addChild(newChild, beforeChild);

    if (madeBoxesNonInline && parent() && isAnonymousBlock() && parent()->isRenderBlock())
        toRenderBlock(parent())->removeLeftoverAnonymousBlock(this);
    // this object may be dead here
}

void RenderBlock::addChild(RenderObject* newChild, RenderObject* beforeChild)
{
    if (continuation() && !isAnonymousBlock())
        return addChildToContinuation(newChild, beforeChild);
    return addChildIgnoringContinuation(newChild, beforeChild);
}

void RenderBlock::addChildIgnoringContinuation(RenderObject* newChild, RenderObject* beforeChild)
{
    if (!isAnonymousBlock() && firstChild() && (firstChild()->isAnonymousColumnsBlock() || firstChild()->isAnonymousColumnSpanBlock()))
        return addChildToAnonymousColumnBlocks(newChild, beforeChild);
    return addChildIgnoringAnonymousColumnBlocks(newChild, beforeChild);
}

static void getInlineRun(RenderObject* start, RenderObject* boundary,
                         RenderObject*& inlineRunStart,
                         RenderObject*& inlineRunEnd)
{
    // Beginning at |start| we find the largest contiguous run of inlines that
    // we can.  We denote the run with start and end points, |inlineRunStart|
    // and |inlineRunEnd|.  Note that these two values may be the same if
    // we encounter only one inline.
    //
    // We skip any non-inlines we encounter as long as we haven't found any
    // inlines yet.
    //
    // |boundary| indicates a non-inclusive boundary point.  Regardless of whether |boundary|
    // is inline or not, we will not include it in a run with inlines before it.  It's as though we encountered
    // a non-inline.
    
    // Start by skipping as many non-inlines as we can.
    RenderObject * curr = start;
    bool sawInline;
    do {
        while (curr && !(curr->isInline() || curr->isFloatingOrPositioned()))
            curr = curr->nextSibling();
        
        inlineRunStart = inlineRunEnd = curr;
        
        if (!curr)
            return; // No more inline children to be found.
        
        sawInline = curr->isInline();
        
        curr = curr->nextSibling();
        while (curr && (curr->isInline() || curr->isFloatingOrPositioned()) && (curr != boundary)) {
            inlineRunEnd = curr;
            if (curr->isInline())
                sawInline = true;
            curr = curr->nextSibling();
        }
    } while (!sawInline);
}

void RenderBlock::deleteLineBoxTree()
{
    m_lineBoxes.deleteLineBoxTree(renderArena());
}

RootInlineBox* RenderBlock::createRootInlineBox() 
{
    return new (renderArena()) RootInlineBox(this);
}

RootInlineBox* RenderBlock::createAndAppendRootInlineBox()
{
    RootInlineBox* rootBox = createRootInlineBox();
    m_lineBoxes.appendLineBox(rootBox);
    return rootBox;
}

void RenderBlock::moveChildTo(RenderBlock* to, RenderObject* child, RenderObject* beforeChild, bool fullRemoveInsert)
{
    ASSERT(this == child->parent());
    ASSERT(!beforeChild || to == beforeChild->parent());
    to->children()->insertChildNode(to, children()->removeChildNode(this, child, fullRemoveInsert), beforeChild, fullRemoveInsert);
}

void RenderBlock::moveChildrenTo(RenderBlock* to, RenderObject* startChild, RenderObject* endChild, RenderObject* beforeChild, bool fullRemoveInsert)
{
    ASSERT(!beforeChild || to == beforeChild->parent());
    RenderObject* nextChild = startChild;
    while (nextChild && nextChild != endChild) {
        RenderObject* child = nextChild;
        nextChild = child->nextSibling();
        to->children()->insertChildNode(to, children()->removeChildNode(this, child, fullRemoveInsert), beforeChild, fullRemoveInsert);
        if (child == endChild)
            return;
    }
}

void RenderBlock::makeChildrenNonInline(RenderObject *insertionPoint)
{    
    // makeChildrenNonInline takes a block whose children are *all* inline and it
    // makes sure that inline children are coalesced under anonymous
    // blocks.  If |insertionPoint| is defined, then it represents the insertion point for
    // the new block child that is causing us to have to wrap all the inlines.  This
    // means that we cannot coalesce inlines before |insertionPoint| with inlines following
    // |insertionPoint|, because the new child is going to be inserted in between the inlines,
    // splitting them.
    ASSERT(isInlineBlockOrInlineTable() || !isInline());
    ASSERT(!insertionPoint || insertionPoint->parent() == this);

    setChildrenInline(false);

    RenderObject *child = firstChild();
    if (!child)
        return;

    deleteLineBoxTree();

    while (child) {
        RenderObject *inlineRunStart, *inlineRunEnd;
        getInlineRun(child, insertionPoint, inlineRunStart, inlineRunEnd);

        if (!inlineRunStart)
            break;

        child = inlineRunEnd->nextSibling();

        RenderBlock* block = createAnonymousBlock();
        children()->insertChildNode(this, block, inlineRunStart);
        moveChildrenTo(block, inlineRunStart, child);
    }

#ifndef NDEBUG
    for (RenderObject *c = firstChild(); c; c = c->nextSibling())
        ASSERT(!c->isInline());
#endif

    repaint();
}

void RenderBlock::removeLeftoverAnonymousBlock(RenderBlock* child)
{
    ASSERT(child->isAnonymousBlock());
    ASSERT(!child->childrenInline());
    
    if (child->continuation() || (child->firstChild() && (child->isAnonymousColumnSpanBlock() || child->isAnonymousColumnsBlock())))
        return;
    
    RenderObject* firstAnChild = child->m_children.firstChild();
    RenderObject* lastAnChild = child->m_children.lastChild();
    if (firstAnChild) {
        RenderObject* o = firstAnChild;
        while (o) {
            o->setParent(this);
            o = o->nextSibling();
        }
        firstAnChild->setPreviousSibling(child->previousSibling());
        lastAnChild->setNextSibling(child->nextSibling());
        if (child->previousSibling())
            child->previousSibling()->setNextSibling(firstAnChild);
        if (child->nextSibling())
            child->nextSibling()->setPreviousSibling(lastAnChild);
            
        if (child == m_children.firstChild())
            m_children.setFirstChild(firstAnChild);
        if (child == m_children.lastChild())
            m_children.setLastChild(lastAnChild);
    } else {
        if (child == m_children.firstChild())
            m_children.setFirstChild(child->nextSibling());
        if (child == m_children.lastChild())
            m_children.setLastChild(child->previousSibling());

        if (child->previousSibling())
            child->previousSibling()->setNextSibling(child->nextSibling());
        if (child->nextSibling())
            child->nextSibling()->setPreviousSibling(child->previousSibling());
    }
    child->setParent(0);
    child->setPreviousSibling(0);
    child->setNextSibling(0);
    
    child->children()->setFirstChild(0);
    child->m_next = 0;

    child->destroy();
}

static bool canMergeContiguousAnonymousBlocks(RenderObject* oldChild, RenderObject* prev, RenderObject* next)
{
    if (oldChild->documentBeingDestroyed() || oldChild->isInline() || oldChild->virtualContinuation())
        return false;

#if ENABLE(DETAILS)
    if (oldChild->parent() && oldChild->parent()->isDetails())
        return false;
#endif

    if ((prev && (!prev->isAnonymousBlock() || toRenderBlock(prev)->continuation() || toRenderBlock(prev)->beingDestroyed()))
        || (next && (!next->isAnonymousBlock() || toRenderBlock(next)->continuation() || toRenderBlock(next)->beingDestroyed())))
        return false;

    // FIXME: This check isn't required when inline run-ins can't be split into continuations.
    if (prev && prev->firstChild() && prev->firstChild()->isInline() && prev->firstChild()->isRunIn())
        return false;

    if ((prev && (prev->isRubyRun() || prev->isRubyBase()))
        || (next && (next->isRubyRun() || next->isRubyBase())))
        return false;

    if (!prev || !next)
        return true;

    // Make sure the types of the anonymous blocks match up.
    return prev->isAnonymousColumnsBlock() == next->isAnonymousColumnsBlock()
           && prev->isAnonymousColumnSpanBlock() == next->isAnonymousColumnSpanBlock();
}

void RenderBlock::removeChild(RenderObject* oldChild)
{
    // If this child is a block, and if our previous and next siblings are
    // both anonymous blocks with inline content, then we can go ahead and
    // fold the inline content back together.
    RenderObject* prev = oldChild->previousSibling();
    RenderObject* next = oldChild->nextSibling();
    bool canMergeAnonymousBlocks = canMergeContiguousAnonymousBlocks(oldChild, prev, next);
    if (canMergeAnonymousBlocks && prev && next) {
        prev->setNeedsLayoutAndPrefWidthsRecalc();
        RenderBlock* nextBlock = toRenderBlock(next);
        RenderBlock* prevBlock = toRenderBlock(prev);
       
        if (prev->childrenInline() != next->childrenInline()) {
            RenderBlock* inlineChildrenBlock = prev->childrenInline() ? prevBlock : nextBlock;
            RenderBlock* blockChildrenBlock = prev->childrenInline() ? nextBlock : prevBlock;
            
            // Place the inline children block inside of the block children block instead of deleting it.
            // In order to reuse it, we have to reset it to just be a generic anonymous block.  Make sure
            // to clear out inherited column properties by just making a new style, and to also clear the
            // column span flag if it is set.
            ASSERT(!inlineChildrenBlock->continuation());
            RefPtr<RenderStyle> newStyle = RenderStyle::createAnonymousStyle(style());
            children()->removeChildNode(this, inlineChildrenBlock, inlineChildrenBlock->hasLayer());
            inlineChildrenBlock->setStyle(newStyle);
            
            // Now just put the inlineChildrenBlock inside the blockChildrenBlock.
            blockChildrenBlock->children()->insertChildNode(blockChildrenBlock, inlineChildrenBlock, prev == inlineChildrenBlock ? blockChildrenBlock->firstChild() : 0,
                                                            inlineChildrenBlock->hasLayer() || blockChildrenBlock->hasLayer());
            next->setNeedsLayoutAndPrefWidthsRecalc();
            
            // inlineChildrenBlock got reparented to blockChildrenBlock, so it is no longer a child
            // of "this". we null out prev or next so that is not used later in the function.
            if (inlineChildrenBlock == prevBlock)
                prev = 0;
            else
                next = 0;
        } else {
            // Take all the children out of the |next| block and put them in
            // the |prev| block.
            nextBlock->moveAllChildrenTo(prevBlock, nextBlock->hasLayer() || prevBlock->hasLayer());        
            
            // Delete the now-empty block's lines and nuke it.
            nextBlock->deleteLineBoxTree();
            nextBlock->destroy();
            next = 0;
        }
    }

    RenderBox::removeChild(oldChild);

    RenderObject* child = prev ? prev : next;
    if (canMergeAnonymousBlocks && child && !child->previousSibling() && !child->nextSibling() && !isDeprecatedFlexibleBox()) {
        // The removal has knocked us down to containing only a single anonymous
        // box.  We can go ahead and pull the content right back up into our
        // box.
        setNeedsLayoutAndPrefWidthsRecalc();
        setChildrenInline(child->childrenInline());
        RenderBlock* anonBlock = toRenderBlock(children()->removeChildNode(this, child, child->hasLayer()));
        anonBlock->moveAllChildrenTo(this, child->hasLayer());
        // Delete the now-empty block's lines and nuke it.
        anonBlock->deleteLineBoxTree();
        anonBlock->destroy();
    }

    if (!firstChild() && !documentBeingDestroyed()) {
        // If this was our last child be sure to clear out our line boxes.
        if (childrenInline())
            lineBoxes()->deleteLineBoxes(renderArena());
    }
}

bool RenderBlock::isSelfCollapsingBlock() const
{
    // We are not self-collapsing if we
    // (a) have a non-zero height according to layout (an optimization to avoid wasting time)
    // (b) are a table,
    // (c) have border/padding,
    // (d) have a min-height
    // (e) have specified that one of our margins can't collapse using a CSS extension
    if (logicalHeight() > 0
        || isTable() || borderAndPaddingLogicalHeight()
        || style()->logicalMinHeight().isPositive()
        || style()->marginBeforeCollapse() == MSEPARATE || style()->marginAfterCollapse() == MSEPARATE)
        return false;

    Length logicalHeightLength = style()->logicalHeight();
    bool hasAutoHeight = logicalHeightLength.isAuto();
    if (logicalHeightLength.isPercent() && !document()->inQuirksMode()) {
        hasAutoHeight = true;
        for (RenderBlock* cb = containingBlock(); !cb->isRenderView(); cb = cb->containingBlock()) {
            if (cb->style()->logicalHeight().isFixed() || cb->isTableCell())
                hasAutoHeight = false;
        }
    }

    // If the height is 0 or auto, then whether or not we are a self-collapsing block depends
    // on whether we have content that is all self-collapsing or not.
    if (hasAutoHeight || ((logicalHeightLength.isFixed() || logicalHeightLength.isPercent()) && logicalHeightLength.isZero())) {
        // If the block has inline children, see if we generated any line boxes.  If we have any
        // line boxes, then we can't be self-collapsing, since we have content.
        if (childrenInline())
            return !firstLineBox();
        
        // Whether or not we collapse is dependent on whether all our normal flow children
        // are also self-collapsing.
        for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
            if (child->isFloatingOrPositioned())
                continue;
            if (!child->isSelfCollapsingBlock())
                return false;
        }
        return true;
    }
    return false;
}

void RenderBlock::startDelayUpdateScrollInfo()
{
    if (gDelayUpdateScrollInfo == 0) {
        ASSERT(!gDelayedUpdateScrollInfoSet);
        gDelayedUpdateScrollInfoSet = new DelayedUpdateScrollInfoSet;
    }
    ASSERT(gDelayedUpdateScrollInfoSet);
    ++gDelayUpdateScrollInfo;
}

void RenderBlock::finishDelayUpdateScrollInfo()
{
    --gDelayUpdateScrollInfo;
    ASSERT(gDelayUpdateScrollInfo >= 0);
    if (gDelayUpdateScrollInfo == 0) {
        ASSERT(gDelayedUpdateScrollInfoSet);

        OwnPtr<DelayedUpdateScrollInfoSet> infoSet(adoptPtr(gDelayedUpdateScrollInfoSet));
        gDelayedUpdateScrollInfoSet = 0;

        for (DelayedUpdateScrollInfoSet::iterator it = infoSet->begin(); it != infoSet->end(); ++it) {
            RenderBlock* block = *it;
            if (block->hasOverflowClip()) {
                block->layer()->updateScrollInfoAfterLayout();
            }
        }
    }
}

void RenderBlock::updateScrollInfoAfterLayout()
{
    if (hasOverflowClip()) {
        if (gDelayUpdateScrollInfo)
            gDelayedUpdateScrollInfoSet->add(this);
        else
            layer()->updateScrollInfoAfterLayout();
    }
}

void RenderBlock::layout()
{
    // Update our first letter info now.
    updateFirstLetter();

    // Table cells call layoutBlock directly, so don't add any logic here.  Put code into
    // layoutBlock().
    layoutBlock(false);
    
    // It's safe to check for control clip here, since controls can never be table cells.
    // If we have a lightweight clip, there can never be any overflow from children.
    if (hasControlClip() && m_overflow)
        clearLayoutOverflow();
}

void RenderBlock::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeight, BlockLayoutPass layoutPass)
{
    ASSERT(needsLayout());

    if (isInline() && !isInlineBlockOrInlineTable()) // Inline <form>s inside various table elements can
        return;                                      // cause us to come in here.  Just bail.

    if (!relayoutChildren && simplifiedLayout())
        return;

    LayoutRepainter repainter(*this, m_everHadLayout && checkForRepaintDuringLayout());

    LayoutUnit oldWidth = logicalWidth();
    LayoutUnit oldColumnWidth = desiredColumnWidth();

    computeLogicalWidth();
    calcColumnWidth();

    m_overflow.clear();

    if (oldWidth != logicalWidth() || oldColumnWidth != desiredColumnWidth())
        relayoutChildren = true;

    // If nothing changed about our floating positioned objects, let's go ahead and try to place them as
    // floats to avoid doing two passes.
    BlockLayoutPass floatsLayoutPass = layoutPass;
    if (floatsLayoutPass == NormalLayoutPass && !relayoutChildren && !positionedFloatsNeedRelayout())
        floatsLayoutPass = PositionedFloatLayoutPass;
    clearFloats(floatsLayoutPass);

    LayoutUnit previousHeight = logicalHeight();
    setLogicalHeight(0);
    bool hasSpecifiedPageLogicalHeight = false;
    bool pageLogicalHeightChanged = false;
    ColumnInfo* colInfo = columnInfo();
    if (hasColumns()) {
        if (!pageLogicalHeight) {
            // We need to go ahead and set our explicit page height if one exists, so that we can
            // avoid doing two layout passes.
            computeLogicalHeight();
            LayoutUnit columnHeight = contentLogicalHeight();
            if (columnHeight > 0) {
                pageLogicalHeight = columnHeight;
                hasSpecifiedPageLogicalHeight = true;
            }
            setLogicalHeight(0);
        }
        if (colInfo->columnHeight() != pageLogicalHeight && m_everHadLayout) {
            colInfo->setColumnHeight(pageLogicalHeight);
            pageLogicalHeightChanged = true;
        }
        
        if (!hasSpecifiedPageLogicalHeight && !pageLogicalHeight)
            colInfo->clearForcedBreaks();
    }

    RenderView* renderView = view();
    LayoutStateMaintainer statePusher(renderView, this, locationOffset(), hasColumns() || hasTransform() || hasReflection() || style()->isFlippedBlocksWritingMode(), pageLogicalHeight, pageLogicalHeightChanged, colInfo);
    
    if (inRenderFlowThread()) {
        // Regions changing widths can force us to relayout our children.
        if (logicalWidthChangedInRegions())
            relayoutChildren = true;
    
        // Set our start and end regions. No regions above or below us will be considered by our children. They are
        // effectively clamped to our region range.
        LayoutUnit oldHeight =  logicalHeight();
        LayoutUnit oldLogicalTop = logicalTop();
        setLogicalHeight(INT_MAX / 2); 
        computeLogicalHeight();
        enclosingRenderFlowThread()->setRegionRangeForBox(this, offsetFromLogicalTopOfFirstPage());
        setLogicalHeight(oldHeight);
        setLogicalTop(oldLogicalTop);
    }

    // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg, to track
    // our current maximal positive and negative margins.  These values are used when we
    // are collapsed with adjacent blocks, so for example, if you have block A and B
    // collapsing together, then you'd take the maximal positive margin from both A and B
    // and subtract it from the maximal negative margin from both A and B to get the
    // true collapsed margin.  This algorithm is recursive, so when we finish layout()
    // our block knows its current maximal positive/negative values.
    //
    // Start out by setting our margin values to our current margins.  Table cells have
    // no margins, so we don't fill in the values for table cells.
    bool isCell = isTableCell();
    if (!isCell) {
        initMaxMarginValues();
        
        setMarginBeforeQuirk(style()->marginBefore().quirk());
        setMarginAfterQuirk(style()->marginAfter().quirk());

        Node* n = node();
        if (n && n->hasTagName(formTag) && static_cast<HTMLFormElement*>(n)->isMalformed()) {
            // See if this form is malformed (i.e., unclosed). If so, don't give the form
            // a bottom margin.
            setMaxMarginAfterValues(0, 0);
        }
        
        setPaginationStrut(0);
    }

    // For overflow:scroll blocks, ensure we have both scrollbars in place always.
    if (scrollsOverflow()) {
        if (style()->overflowX() == OSCROLL)
            layer()->setHasHorizontalScrollbar(true);
        if (style()->overflowY() == OSCROLL)
            layer()->setHasVerticalScrollbar(true);
    }

    LayoutUnit repaintLogicalTop = 0;
    LayoutUnit repaintLogicalBottom = 0;
    LayoutUnit maxFloatLogicalBottom = 0;
    if (!firstChild() && !isAnonymousBlock())
        setChildrenInline(true);
    if (childrenInline())
        layoutInlineChildren(relayoutChildren, repaintLogicalTop, repaintLogicalBottom);
    else
        layoutBlockChildren(relayoutChildren, maxFloatLogicalBottom);

    // Expand our intrinsic height to encompass floats.
    LayoutUnit toAdd = borderAfter() + paddingAfter() + scrollbarLogicalHeight();
    if (lowestFloatLogicalBottom() > (logicalHeight() - toAdd) && expandsToEncloseOverhangingFloats())
        setLogicalHeight(lowestFloatLogicalBottom() + toAdd);
    
    if (layoutColumns(hasSpecifiedPageLogicalHeight, pageLogicalHeight, statePusher))
        return;
 
    // Calculate our new height.
    LayoutUnit oldHeight = logicalHeight();
    LayoutUnit oldClientAfterEdge = clientLogicalBottom();
    computeLogicalHeight();
    LayoutUnit newHeight = logicalHeight();
    if (oldHeight != newHeight) {
        if (oldHeight > newHeight && maxFloatLogicalBottom > newHeight && !childrenInline()) {
            // One of our children's floats may have become an overhanging float for us. We need to look for it.
            for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
                if (child->isBlockFlow() && !child->isFloatingOrPositioned()) {
                    RenderBlock* block = toRenderBlock(child);
                    if (block->lowestFloatLogicalBottomIncludingPositionedFloats() + block->logicalTop() > newHeight)
                        addOverhangingFloats(block, false);
                }
            }
        }
    }

    if (previousHeight != newHeight)
        relayoutChildren = true;

    bool needAnotherLayoutPass = layoutPositionedObjects(relayoutChildren || isRoot());

    if (inRenderFlowThread())
        enclosingRenderFlowThread()->setRegionRangeForBox(this, offsetFromLogicalTopOfFirstPage());

    // Add overflow from children (unless we're multi-column, since in that case all our child overflow is clipped anyway).
    computeOverflow(oldClientAfterEdge);
    
    statePusher.pop();

    if (renderView->layoutState()->m_pageLogicalHeight)
        setPageLogicalOffset(renderView->layoutState()->pageLogicalOffset(logicalTop()));

    updateLayerTransform();

    // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
    // we overflow or not.
    updateScrollInfoAfterLayout();

    // FIXME: This repaint logic should be moved into a separate helper function!
    // Repaint with our new bounds if they are different from our old bounds.
    bool didFullRepaint = repainter.repaintAfterLayout();
    if (!didFullRepaint && repaintLogicalTop != repaintLogicalBottom && (style()->visibility() == VISIBLE || enclosingLayer()->hasVisibleContent())) {
        // FIXME: We could tighten up the left and right invalidation points if we let layoutInlineChildren fill them in based off the particular lines
        // it had to lay out.  We wouldn't need the hasOverflowClip() hack in that case either.
        LayoutUnit repaintLogicalLeft = logicalLeftVisualOverflow();
        LayoutUnit repaintLogicalRight = logicalRightVisualOverflow();
        if (hasOverflowClip()) {
            // If we have clipped overflow, we should use layout overflow as well, since visual overflow from lines didn't propagate to our block's overflow.
            // Note the old code did this as well but even for overflow:visible.  The addition of hasOverflowClip() at least tightens up the hack a bit.
            // layoutInlineChildren should be patched to compute the entire repaint rect.
            repaintLogicalLeft = min(repaintLogicalLeft, logicalLeftLayoutOverflow());
            repaintLogicalRight = max(repaintLogicalRight, logicalRightLayoutOverflow());
        }
        
        LayoutRect repaintRect;
        if (isHorizontalWritingMode())
            repaintRect = LayoutRect(repaintLogicalLeft, repaintLogicalTop, repaintLogicalRight - repaintLogicalLeft, repaintLogicalBottom - repaintLogicalTop);
        else
            repaintRect = LayoutRect(repaintLogicalTop, repaintLogicalLeft, repaintLogicalBottom - repaintLogicalTop, repaintLogicalRight - repaintLogicalLeft);

        // The repaint rect may be split across columns, in which case adjustRectForColumns() will return the union.
        adjustRectForColumns(repaintRect);

        repaintRect.inflate(maximalOutlineSize(PaintPhaseOutline));
        
        if (hasOverflowClip()) {
            // Adjust repaint rect for scroll offset
            repaintRect.move(-layer()->scrolledContentOffset());

            // Don't allow this rect to spill out of our overflow box.
            repaintRect.intersect(LayoutRect(LayoutPoint(), size()));
        }

        // Make sure the rect is still non-empty after intersecting for overflow above
        if (!repaintRect.isEmpty()) {
            // FIXME: Might need rounding once we switch to float, see https://bugs.webkit.org/show_bug.cgi?id=64021
            repaintRectangle(repaintRect); // We need to do a partial repaint of our content.
            if (hasReflection())
                repaintRectangle(reflectedRect(repaintRect));
        }
    }
    
    if (needAnotherLayoutPass && layoutPass == NormalLayoutPass) {
        setChildNeedsLayout(true, false);
        layoutBlock(false, pageLogicalHeight, PositionedFloatLayoutPass);
    } else
        setNeedsLayout(false);
}

void RenderBlock::addOverflowFromChildren()
{
    if (!hasColumns()) {
        if (childrenInline())
            addOverflowFromInlineChildren();
        else
            addOverflowFromBlockChildren();
    } else {
        ColumnInfo* colInfo = columnInfo();
        if (columnCount(colInfo)) {
            LayoutRect lastRect = columnRectAt(colInfo, columnCount(colInfo) - 1);
            if (isHorizontalWritingMode()) {
                LayoutUnit overflowLeft = !style()->isLeftToRightDirection() ? min<LayoutUnit>(0, lastRect.x()) : 0;
                LayoutUnit overflowRight = style()->isLeftToRightDirection() ? max(width(), lastRect.maxX()) : 0;
                LayoutUnit overflowHeight = borderBefore() + paddingBefore() + colInfo->columnHeight();
                addLayoutOverflow(LayoutRect(overflowLeft, 0, overflowRight - overflowLeft, overflowHeight));
                if (!hasOverflowClip())
                    addVisualOverflow(LayoutRect(overflowLeft, 0, overflowRight - overflowLeft, overflowHeight));
            } else {
                LayoutRect lastRect = columnRectAt(colInfo, columnCount(colInfo) - 1);
                LayoutUnit overflowTop = !style()->isLeftToRightDirection() ? min<LayoutUnit>(0, lastRect.y()) : 0;
                LayoutUnit overflowBottom = style()->isLeftToRightDirection() ? max(height(), lastRect.maxY()) : 0;
                LayoutUnit overflowWidth = borderBefore() + paddingBefore() + colInfo->columnHeight();
                addLayoutOverflow(LayoutRect(0, overflowTop, overflowWidth, overflowBottom - overflowTop));
                if (!hasOverflowClip())
                    addVisualOverflow(LayoutRect(0, overflowTop, overflowWidth, overflowBottom - overflowTop));
            }
        }
    }
}

void RenderBlock::computeOverflow(LayoutUnit oldClientAfterEdge, bool recomputeFloats)
{
    // Add overflow from children.
    addOverflowFromChildren();

    if (!hasColumns() && (recomputeFloats || isRoot() || expandsToEncloseOverhangingFloats() || hasSelfPaintingLayer()))
        addOverflowFromFloats();

    // Add in the overflow from positioned objects.
    addOverflowFromPositionedObjects();

    if (hasOverflowClip()) {
        // When we have overflow clip, propagate the original spillout since it will include collapsed bottom margins
        // and bottom padding.  Set the axis we don't care about to be 1, since we want this overflow to always
        // be considered reachable.
        LayoutRect clientRect(clientBoxRect());
        LayoutRect rectToApply;
        if (isHorizontalWritingMode())
            rectToApply = LayoutRect(clientRect.x(), clientRect.y(), 1, max<LayoutUnit>(0, oldClientAfterEdge - clientRect.y()));
        else
            rectToApply = LayoutRect(clientRect.x(), clientRect.y(), max<LayoutUnit>(0, oldClientAfterEdge - clientRect.x()), 1);
        addLayoutOverflow(rectToApply);
    }
        
    // Add visual overflow from box-shadow and border-image-outset.
    addBoxShadowAndBorderOverflow();
}

void RenderBlock::addOverflowFromBlockChildren()
{
    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {
        if (!child->isFloatingOrPositioned())
            addOverflowFromChild(child);
    }
}

void RenderBlock::addOverflowFromFloats()
{
    if (!m_floatingObjects)
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* r = *it;
        if (r->m_isDescendant && !r->m_renderer->isPositioned())
            addOverflowFromChild(r->m_renderer, IntSize(xPositionForFloatIncludingMargin(r), yPositionForFloatIncludingMargin(r)));
    }
    return;
}

void RenderBlock::addOverflowFromPositionedObjects()
{
    if (!m_positionedObjects)
        return;

    RenderBox* positionedObject;
    Iterator end = m_positionedObjects->end();
    for (Iterator it = m_positionedObjects->begin(); it != end; ++it) {
        positionedObject = *it;
        
        // Fixed positioned elements don't contribute to layout overflow, since they don't scroll with the content.
        if (positionedObject->style()->position() != FixedPosition)
            addOverflowFromChild(positionedObject);
    }
}

bool RenderBlock::expandsToEncloseOverhangingFloats() const
{
    return isInlineBlockOrInlineTable() || isFloatingOrPositioned() || hasOverflowClip() || (parent() && parent()->isDeprecatedFlexibleBox())
           || hasColumns() || isTableCell() || isFieldset() || isWritingModeRoot() || isRoot();
}

void RenderBlock::adjustPositionedBlock(RenderBox* child, const MarginInfo& marginInfo)
{
    bool isHorizontal = isHorizontalWritingMode();
    bool hasStaticBlockPosition = child->style()->hasStaticBlockPosition(isHorizontal);
    
    LayoutUnit logicalTop = logicalHeight();
    setStaticInlinePositionForChild(child, logicalTop, startOffsetForContent(logicalTop));

    if (!marginInfo.canCollapseWithMarginBefore()) {
        child->computeBlockDirectionMargins(this);
        LayoutUnit marginBefore = marginBeforeForChild(child);
        LayoutUnit collapsedBeforePos = marginInfo.positiveMargin();
        LayoutUnit collapsedBeforeNeg = marginInfo.negativeMargin();
        if (marginBefore > 0) {
            if (marginBefore > collapsedBeforePos)
                collapsedBeforePos = marginBefore;
        } else {
            if (-marginBefore > collapsedBeforeNeg)
                collapsedBeforeNeg = -marginBefore;
        }
        logicalTop += (collapsedBeforePos - collapsedBeforeNeg) - marginBefore;
    }
    
    RenderLayer* childLayer = child->layer();
    if (childLayer->staticBlockPosition() != logicalTop) {
        childLayer->setStaticBlockPosition(logicalTop);
        if (hasStaticBlockPosition)
            child->setChildNeedsLayout(true, false);
    }
}

void RenderBlock::adjustFloatingBlock(const MarginInfo& marginInfo)
{
    // The float should be positioned taking into account the bottom margin
    // of the previous flow.  We add that margin into the height, get the
    // float positioned properly, and then subtract the margin out of the
    // height again.  In the case of self-collapsing blocks, we always just
    // use the top margins, since the self-collapsing block collapsed its
    // own bottom margin into its top margin.
    //
    // Note also that the previous flow may collapse its margin into the top of
    // our block.  If this is the case, then we do not add the margin in to our
    // height when computing the position of the float.   This condition can be tested
    // for by simply calling canCollapseWithMarginBefore.  See
    // http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/046.html for
    // an example of this scenario.
    LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? 0 : marginInfo.margin();
    setLogicalHeight(logicalHeight() + marginOffset);
    positionNewFloats();
    setLogicalHeight(logicalHeight() - marginOffset);
}

bool RenderBlock::handleSpecialChild(RenderBox* child, const MarginInfo& marginInfo)
{
    // Handle in the given order
    return handlePositionedChild(child, marginInfo)
        || handleFloatingChild(child, marginInfo)
        || handleRunInChild(child);
}


bool RenderBlock::handlePositionedChild(RenderBox* child, const MarginInfo& marginInfo)
{
    if (child->isPositioned()) {
        child->containingBlock()->insertPositionedObject(child);
        adjustPositionedBlock(child, marginInfo);
        return true;
    }
    return false;
}

bool RenderBlock::handleFloatingChild(RenderBox* child, const MarginInfo& marginInfo)
{
    if (child->isFloating()) {
        insertFloatingObject(child);
        adjustFloatingBlock(marginInfo);
        return true;
    }
    return false;
}

bool RenderBlock::handleRunInChild(RenderBox* child)
{
    // See if we have a run-in element with inline children.  If the
    // children aren't inline, then just treat the run-in as a normal
    // block.
    if (!child->isRunIn() || !child->childrenInline())
        return false;
    // FIXME: We don't handle non-block elements with run-in for now.
    if (!child->isRenderBlock())
        return false;

    RenderBlock* blockRunIn = toRenderBlock(child);
    RenderObject* curr = blockRunIn->nextSibling();
    if (!curr || !curr->isRenderBlock() || !curr->childrenInline() || curr->isRunIn() || curr->isAnonymous() || curr->isFloatingOrPositioned())
        return false;

    RenderBlock* currBlock = toRenderBlock(curr);

    // Remove the old child.
    children()->removeChildNode(this, blockRunIn);

    // Create an inline.
    Node* runInNode = blockRunIn->node();
    RenderInline* inlineRunIn = new (renderArena()) RenderInline(runInNode ? runInNode : document());
    inlineRunIn->setStyle(blockRunIn->style());

    bool runInIsGenerated = child->style()->styleType() == BEFORE || child->style()->styleType() == AFTER;

    // Move the nodes from the old child to the new child, but skip any :before/:after content.  It has already
    // been regenerated by the new inline.
    for (RenderObject* runInChild = blockRunIn->firstChild(); runInChild;) {
        RenderObject* nextSibling = runInChild->nextSibling();
        if (runInIsGenerated || (runInChild->style()->styleType() != BEFORE && runInChild->style()->styleType() != AFTER)) {
            blockRunIn->children()->removeChildNode(blockRunIn, runInChild, false);
            inlineRunIn->addChild(runInChild); // Use addChild instead of appendChildNode since it handles correct placement of the children relative to :after-generated content.
        }
        runInChild = nextSibling;
    }

    // Now insert the new child under |currBlock|. Use addChild instead of insertChildNode since it handles correct placement of the children, esp where we cannot insert
    // anything before the first child. e.g. details tag. See https://bugs.webkit.org/show_bug.cgi?id=58228.
    currBlock->addChild(inlineRunIn, currBlock->firstChild());
    
    // If the run-in had an element, we need to set the new renderer.
    if (runInNode)
        runInNode->setRenderer(inlineRunIn);

    // Destroy the block run-in, which includes deleting its line box tree.
    blockRunIn->deleteLineBoxTree();
    blockRunIn->destroy();

    // The block acts like an inline, so just null out its
    // position.
    
    return true;
}

LayoutUnit RenderBlock::collapseMargins(RenderBox* child, MarginInfo& marginInfo)
{
    // Get the four margin values for the child and cache them.
    const MarginValues childMargins = marginValuesForChild(child);

    // Get our max pos and neg top margins.
    LayoutUnit posTop = childMargins.positiveMarginBefore();
    LayoutUnit negTop = childMargins.negativeMarginBefore();

    // For self-collapsing blocks, collapse our bottom margins into our
    // top to get new posTop and negTop values.
    if (child->isSelfCollapsingBlock()) {
        posTop = max(posTop, childMargins.positiveMarginAfter());
        negTop = max(negTop, childMargins.negativeMarginAfter());
    }
    
    // See if the top margin is quirky. We only care if this child has
    // margins that will collapse with us.
    bool topQuirk = child->isMarginBeforeQuirk() || style()->marginBeforeCollapse() == MDISCARD;

    if (marginInfo.canCollapseWithMarginBefore()) {
        // This child is collapsing with the top of the
        // block.  If it has larger margin values, then we need to update
        // our own maximal values.
        if (!document()->inQuirksMode() || !marginInfo.quirkContainer() || !topQuirk)
            setMaxMarginBeforeValues(max(posTop, maxPositiveMarginBefore()), max(negTop, maxNegativeMarginBefore()));

        // The minute any of the margins involved isn't a quirk, don't
        // collapse it away, even if the margin is smaller (www.webreference.com
        // has an example of this, a <dt> with 0.8em author-specified inside
        // a <dl> inside a <td>.
        if (!marginInfo.determinedMarginBeforeQuirk() && !topQuirk && (posTop - negTop)) {
            setMarginBeforeQuirk(false);
            marginInfo.setDeterminedMarginBeforeQuirk(true);
        }

        if (!marginInfo.determinedMarginBeforeQuirk() && topQuirk && !marginBefore())
            // We have no top margin and our top child has a quirky margin.
            // We will pick up this quirky margin and pass it through.
            // This deals with the <td><div><p> case.
            // Don't do this for a block that split two inlines though.  You do
            // still apply margins in this case.
            setMarginBeforeQuirk(true);
    }

    if (marginInfo.quirkContainer() && marginInfo.atBeforeSideOfBlock() && (posTop - negTop))
        marginInfo.setMarginBeforeQuirk(topQuirk);

    LayoutUnit beforeCollapseLogicalTop = logicalHeight();
    LayoutUnit logicalTop = beforeCollapseLogicalTop;
    if (child->isSelfCollapsingBlock()) {
        // This child has no height.  We need to compute our
        // position before we collapse the child's margins together,
        // so that we can get an accurate position for the zero-height block.
        LayoutUnit collapsedBeforePos = max(marginInfo.positiveMargin(), childMargins.positiveMarginBefore());
        LayoutUnit collapsedBeforeNeg = max(marginInfo.negativeMargin(), childMargins.negativeMarginBefore());
        marginInfo.setMargin(collapsedBeforePos, collapsedBeforeNeg);
        
        // Now collapse the child's margins together, which means examining our
        // bottom margin values as well. 
        marginInfo.setPositiveMarginIfLarger(childMargins.positiveMarginAfter());
        marginInfo.setNegativeMarginIfLarger(childMargins.negativeMarginAfter());

        if (!marginInfo.canCollapseWithMarginBefore())
            // We need to make sure that the position of the self-collapsing block
            // is correct, since it could have overflowing content
            // that needs to be positioned correctly (e.g., a block that
            // had a specified height of 0 but that actually had subcontent).
            logicalTop = logicalHeight() + collapsedBeforePos - collapsedBeforeNeg;
    }
    else {
        if (child->style()->marginBeforeCollapse() == MSEPARATE) {
            setLogicalHeight(logicalHeight() + marginInfo.margin() + marginBeforeForChild(child));
            logicalTop = logicalHeight();
        }
        else if (!marginInfo.atBeforeSideOfBlock() ||
            (!marginInfo.canCollapseMarginBeforeWithChildren()
             && (!document()->inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.marginBeforeQuirk()))) {
            // We're collapsing with a previous sibling's margins and not
            // with the top of the block.
            setLogicalHeight(logicalHeight() + max(marginInfo.positiveMargin(), posTop) - max(marginInfo.negativeMargin(), negTop));
            logicalTop = logicalHeight();
        }

        marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
        marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());

        if (marginInfo.margin())
            marginInfo.setMarginAfterQuirk(child->isMarginAfterQuirk() || style()->marginAfterCollapse() == MDISCARD);
    }
    
    // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
    // collapsed into the page edge.
    LayoutState* layoutState = view()->layoutState();
    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop
        && hasNextPage(beforeCollapseLogicalTop)) {
        LayoutUnit oldLogicalTop = logicalTop;
        logicalTop = min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
        setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
    }
    return logicalTop;
}

LayoutUnit RenderBlock::clearFloatsIfNeeded(RenderBox* child, MarginInfo& marginInfo, int oldTopPosMargin, int oldTopNegMargin, int yPos)
{
    LayoutUnit heightIncrease = getClearDelta(child, yPos);
    if (!heightIncrease)
        return yPos;

    if (child->isSelfCollapsingBlock()) {
        // For self-collapsing blocks that clear, they can still collapse their
        // margins with following siblings.  Reset the current margins to represent
        // the self-collapsing block's margins only.
        // CSS2.1 states:
        // "An element that has had clearance applied to it never collapses its top margin with its parent block's bottom margin.
        // Therefore if we are at the bottom of the block, let's go ahead and reset margins to only include the
        // self-collapsing block's bottom margin.
        bool atBottomOfBlock = true;
        for (RenderBox* curr = child->nextSiblingBox(); curr && atBottomOfBlock; curr = curr->nextSiblingBox()) {
            if (!curr->isFloatingOrPositioned())
                atBottomOfBlock = false;
        }
        
        MarginValues childMargins = marginValuesForChild(child);
        if (atBottomOfBlock) {
            marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
            marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());
        } else {
            marginInfo.setPositiveMargin(max(childMargins.positiveMarginBefore(), childMargins.positiveMarginAfter()));
            marginInfo.setNegativeMargin(max(childMargins.negativeMarginBefore(), childMargins.negativeMarginAfter()));
        }
        
        // Adjust our height such that we are ready to be collapsed with subsequent siblings (or the bottom
        // of the parent block).
        setLogicalHeight(child->y() - max<LayoutUnit>(0, marginInfo.margin()));
    } else
        // Increase our height by the amount we had to clear.
        setLogicalHeight(height() + heightIncrease);
    
    if (marginInfo.canCollapseWithMarginBefore()) {
        // We can no longer collapse with the top of the block since a clear
        // occurred.  The empty blocks collapse into the cleared block.
        // FIXME: This isn't quite correct.  Need clarification for what to do
        // if the height the cleared block is offset by is smaller than the
        // margins involved.
        setMaxMarginBeforeValues(oldTopPosMargin, oldTopNegMargin);
        marginInfo.setAtBeforeSideOfBlock(false);
    }
    
    return yPos + heightIncrease;
}

LayoutUnit RenderBlock::estimateLogicalTopPosition(RenderBox* child, const MarginInfo& marginInfo, LayoutUnit& estimateWithoutPagination)
{
    // FIXME: We need to eliminate the estimation of vertical position, because when it's wrong we sometimes trigger a pathological
    // relayout if there are intruding floats.
    LayoutUnit logicalTopEstimate = logicalHeight();
    if (!marginInfo.canCollapseWithMarginBefore()) {
        LayoutUnit childMarginBefore = child->selfNeedsLayout() ? marginBeforeForChild(child) : collapsedMarginBeforeForChild(child);
        logicalTopEstimate += max(marginInfo.margin(), childMarginBefore);
    }

    // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
    // page.
    LayoutState* layoutState = view()->layoutState();
    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight()
        && hasNextPage(logicalHeight()))
        logicalTopEstimate = min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));

    logicalTopEstimate += getClearDelta(child, logicalTopEstimate);
    
    estimateWithoutPagination = logicalTopEstimate;

    if (layoutState->isPaginated()) {
        // If the object has a page or column break value of "before", then we should shift to the top of the next page.
        logicalTopEstimate = applyBeforeBreak(child, logicalTopEstimate);
    
        // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
        logicalTopEstimate = adjustForUnsplittableChild(child, logicalTopEstimate);
        
        if (!child->selfNeedsLayout() && child->isRenderBlock())
            logicalTopEstimate += toRenderBlock(child)->paginationStrut();
    }

    return logicalTopEstimate;
}

LayoutUnit RenderBlock::computeStartPositionDeltaForChildAvoidingFloats(const RenderBox* child, LayoutUnit childMarginStart,
    LayoutUnit childLogicalWidth, RenderRegion* region, LayoutUnit offsetFromLogicalTopOfFirstPage)
{
    LayoutUnit startPosition = startOffsetForContent(region, offsetFromLogicalTopOfFirstPage);

    // Add in our start margin.
    LayoutUnit oldPosition = startPosition + childMarginStart;
    LayoutUnit newPosition = oldPosition;

    LayoutUnit blockOffset = logicalTopForChild(child);
    if (region)
        blockOffset = max(blockOffset, blockOffset + (region->offsetFromLogicalTopOfFirstPage() - offsetFromLogicalTopOfFirstPage));

    LayoutUnit startOff = startOffsetForLine(blockOffset, false, region, offsetFromLogicalTopOfFirstPage);
    if (style()->textAlign() != WEBKIT_CENTER && !child->style()->marginStartUsing(style()).isAuto()) {
        if (childMarginStart < 0)
            startOff += childMarginStart;
        newPosition = max(newPosition, startOff); // Let the float sit in the child's margin if it can fit.
        // FIXME: Needs to use epsilon once we switch to float, see https://bugs.webkit.org/show_bug.cgi?id=64021
    } else if (startOff != startPosition) {
        // The object is shifting to the "end" side of the block. The object might be centered, so we need to
        // recalculate our inline direction margins. Note that the containing block content
        // width computation will take into account the delta between |startOff| and |startPosition|
        // so that we can just pass the content width in directly to the |computeMarginsInContainingBlockInlineDirection|
        // function.
        LayoutUnit oldMarginStart = marginStartForChild(child);
        LayoutUnit oldMarginEnd = marginEndForChild(child);
        RenderBox* mutableChild = const_cast<RenderBox*>(child);
        mutableChild->computeInlineDirectionMargins(this,
            availableLogicalWidthForLine(blockOffset, false, region, offsetFromLogicalTopOfFirstPage), childLogicalWidth);
        newPosition = startOff + marginStartForChild(child);
        if (inRenderFlowThread()) {
            setMarginStartForChild(mutableChild, oldMarginStart);
            setMarginEndForChild(mutableChild, oldMarginEnd);
        }
    }
    
    return newPosition - oldPosition;
}

void RenderBlock::determineLogicalLeftPositionForChild(RenderBox* child)
{
    LayoutUnit startPosition = borderStart() + paddingStart();
    LayoutUnit totalAvailableLogicalWidth = borderAndPaddingLogicalWidth() + availableLogicalWidth();

    // Add in our start margin.
    LayoutUnit childMarginStart = marginStartForChild(child);
    LayoutUnit newPosition = startPosition + childMarginStart;
        
    // Some objects (e.g., tables, horizontal rules, overflow:auto blocks) avoid floats.  They need
    // to shift over as necessary to dodge any floats that might get in the way.
    if (child->avoidsFloats() && containsFloats() && !inRenderFlowThread())
        newPosition += computeStartPositionDeltaForChildAvoidingFloats(child, marginStartForChild(child), logicalWidthForChild(child));

    setLogicalLeftForChild(child, style()->isLeftToRightDirection() ? newPosition : totalAvailableLogicalWidth - newPosition - logicalWidthForChild(child), ApplyLayoutDelta);
}

void RenderBlock::setCollapsedBottomMargin(const MarginInfo& marginInfo)
{
    if (marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()) {
        // Update our max pos/neg bottom margins, since we collapsed our bottom margins
        // with our children.
        setMaxMarginAfterValues(max(maxPositiveMarginAfter(), marginInfo.positiveMargin()), max(maxNegativeMarginAfter(), marginInfo.negativeMargin()));

        if (!marginInfo.marginAfterQuirk())
            setMarginAfterQuirk(false);

        if (marginInfo.marginAfterQuirk() && marginAfter() == 0)
            // We have no bottom margin and our last child has a quirky margin.
            // We will pick up this quirky margin and pass it through.
            // This deals with the <td><div><p> case.
            setMarginAfterQuirk(true);
    }
}

void RenderBlock::handleAfterSideOfBlock(LayoutUnit beforeSide, LayoutUnit afterSide, MarginInfo& marginInfo)
{
    marginInfo.setAtAfterSideOfBlock(true);

    // If we can't collapse with children then go ahead and add in the bottom margin.
    if (!marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()
        && (!document()->inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.marginAfterQuirk()))
        setLogicalHeight(logicalHeight() + marginInfo.margin());
        
    // Now add in our bottom border/padding.
    setLogicalHeight(logicalHeight() + afterSide);

    // Negative margins can cause our height to shrink below our minimal height (border/padding).
    // If this happens, ensure that the computed height is increased to the minimal height.
    setLogicalHeight(max(logicalHeight(), beforeSide + afterSide));

    // Update our bottom collapsed margin info.
    setCollapsedBottomMargin(marginInfo);
}

void RenderBlock::setLogicalLeftForChild(RenderBox* child, LayoutUnit logicalLeft, ApplyLayoutDeltaMode applyDelta)
{
    if (isHorizontalWritingMode()) {
        if (applyDelta == ApplyLayoutDelta)
            view()->addLayoutDelta(LayoutSize(child->x() - logicalLeft, 0));
        child->setX(logicalLeft);
    } else {
        if (applyDelta == ApplyLayoutDelta)
            view()->addLayoutDelta(LayoutSize(0, child->y() - logicalLeft));
        child->setY(logicalLeft);
    }
}

void RenderBlock::setLogicalTopForChild(RenderBox* child, LayoutUnit logicalTop, ApplyLayoutDeltaMode applyDelta)
{
    if (isHorizontalWritingMode()) {
        if (applyDelta == ApplyLayoutDelta)
            view()->addLayoutDelta(LayoutSize(0, child->y() - logicalTop));
        child->setY(logicalTop);
    } else {
        if (applyDelta == ApplyLayoutDelta)
            view()->addLayoutDelta(LayoutSize(child->x() - logicalTop, 0));
        child->setX(logicalTop);
    }
}

void RenderBlock::layoutBlockChildren(bool relayoutChildren, LayoutUnit& maxFloatLogicalBottom)
{
    if (gPercentHeightDescendantsMap) {
        if (HashSet<RenderBox*>* descendants = gPercentHeightDescendantsMap->get(this)) {
            HashSet<RenderBox*>::iterator end = descendants->end();
            for (HashSet<RenderBox*>::iterator it = descendants->begin(); it != end; ++it) {
                RenderBox* box = *it;
                while (box != this) {
                    if (box->normalChildNeedsLayout())
                        break;
                    box->setChildNeedsLayout(true, false);
                    box = box->containingBlock();
                    ASSERT(box);
                    if (!box)
                        break;
                }
            }
        }
    }

    LayoutUnit beforeEdge = borderBefore() + paddingBefore();
    LayoutUnit afterEdge = borderAfter() + paddingAfter() + scrollbarLogicalHeight();

    setLogicalHeight(beforeEdge);

    // The margin struct caches all our current margin collapsing state.  The compact struct caches state when we encounter compacts,
    MarginInfo marginInfo(this, beforeEdge, afterEdge);

    // Fieldsets need to find their legend and position it inside the border of the object.
    // The legend then gets skipped during normal layout.  The same is true for ruby text.
    // It doesn't get included in the normal layout process but is instead skipped.
    RenderObject* childToExclude = layoutSpecialExcludedChild(relayoutChildren);

    LayoutUnit previousFloatLogicalBottom = 0;
    maxFloatLogicalBottom = 0;

    RenderBox* next = firstChildBox();

    while (next) {
        RenderBox* child = next;
        next = child->nextSiblingBox();

        if (childToExclude == child)
            continue; // Skip this child, since it will be positioned by the specialized subclass (fieldsets and ruby runs).

        // Make sure we layout children if they need it.
        // FIXME: Technically percentage height objects only need a relayout if their percentage isn't going to be turned into
        // an auto value.  Add a method to determine this, so that we can avoid the relayout.
        if (relayoutChildren || ((child->style()->logicalHeight().isPercent() || child->style()->logicalMinHeight().isPercent() || child->style()->logicalMaxHeight().isPercent()) && !isRenderView()))
            child->setChildNeedsLayout(true, false);

        // If relayoutChildren is set and the child has percentage padding or an embedded content box, we also need to invalidate the childs pref widths.
        if (relayoutChildren && child->needsPreferredWidthsRecalculation())
            child->setPreferredLogicalWidthsDirty(true, false);

        // Handle the four types of special elements first.  These include positioned content, floating content, compacts and
        // run-ins.  When we encounter these four types of objects, we don't actually lay them out as normal flow blocks.
        if (handleSpecialChild(child, marginInfo))
            continue;

        // Lay out the child.
        layoutBlockChild(child, marginInfo, previousFloatLogicalBottom, maxFloatLogicalBottom);
    }
    
    // Now do the handling of the bottom of the block, adding in our bottom border/padding and
    // determining the correct collapsed bottom margin information.
    handleAfterSideOfBlock(beforeEdge, afterEdge, marginInfo);
}

void RenderBlock::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo, LayoutUnit& previousFloatLogicalBottom, LayoutUnit& maxFloatLogicalBottom)
{
    LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
    LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();

    // The child is a normal flow object.  Compute the margins we will use for collapsing now.
    child->computeBlockDirectionMargins(this);

    // Do not allow a collapse if the margin-before-collapse style is set to SEPARATE.
    if (child->style()->marginBeforeCollapse() == MSEPARATE) {
        marginInfo.setAtBeforeSideOfBlock(false);
        marginInfo.clearMargin();
    }

    // Try to guess our correct logical top position.  In most cases this guess will
    // be correct.  Only if we're wrong (when we compute the real logical top position)
    // will we have to potentially relayout.
    LayoutUnit estimateWithoutPagination;
    LayoutUnit logicalTopEstimate = estimateLogicalTopPosition(child, marginInfo, estimateWithoutPagination);

    // Cache our old rect so that we can dirty the proper repaint rects if the child moves.
    LayoutRect oldRect(child->x(), child->y() , child->width(), child->height());
    LayoutUnit oldLogicalTop = logicalTopForChild(child);

#ifndef NDEBUG
    LayoutSize oldLayoutDelta = view()->layoutDelta();
#endif
    // Go ahead and position the child as though it didn't collapse with the top.
    setLogicalTopForChild(child, logicalTopEstimate, ApplyLayoutDelta);

    RenderBlock* childRenderBlock = child->isRenderBlock() ? toRenderBlock(child) : 0;
    bool markDescendantsWithFloats = false;
    if (logicalTopEstimate != oldLogicalTop && !child->avoidsFloats() && childRenderBlock && childRenderBlock->containsFloats())
        markDescendantsWithFloats = true;
    else if (!child->avoidsFloats() || child->shrinkToAvoidFloats()) {
        // If an element might be affected by the presence of floats, then always mark it for
        // layout.
        LayoutUnit fb = max(previousFloatLogicalBottom, lowestFloatLogicalBottomIncludingPositionedFloats());
        if (fb > logicalTopEstimate)
            markDescendantsWithFloats = true;
    }

    if (childRenderBlock) {
        if (markDescendantsWithFloats)
            childRenderBlock->markAllDescendantsWithFloatsForLayout();
        if (!child->isWritingModeRoot())
            previousFloatLogicalBottom = max(previousFloatLogicalBottom, oldLogicalTop + childRenderBlock->lowestFloatLogicalBottomIncludingPositionedFloats());
    }

    if (!child->needsLayout())
        child->markForPaginationRelayoutIfNeeded();

    bool childHadLayout = child->m_everHadLayout;
    bool childNeededLayout = child->needsLayout();
    if (childNeededLayout)
        child->layout();

    // Cache if we are at the top of the block right now.
    bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();

    // Now determine the correct ypos based off examination of collapsing margin
    // values.
    LayoutUnit logicalTopBeforeClear = collapseMargins(child, marginInfo);

    // Now check for clear.
    LayoutUnit logicalTopAfterClear = clearFloatsIfNeeded(child, marginInfo, oldPosMarginBefore, oldNegMarginBefore, logicalTopBeforeClear);
    
    bool paginated = view()->layoutState()->isPaginated();
    if (paginated)
        logicalTopAfterClear = adjustBlockChildForPagination(logicalTopAfterClear, estimateWithoutPagination, child,
            atBeforeSideOfBlock && logicalTopBeforeClear == logicalTopAfterClear);

    setLogicalTopForChild(child, logicalTopAfterClear, ApplyLayoutDelta);

    // Now we have a final top position.  See if it really does end up being different from our estimate.
    if (logicalTopAfterClear != logicalTopEstimate) {
        if (child->shrinkToAvoidFloats()) {
            // The child's width depends on the line width.
            // When the child shifts to clear an item, its width can
            // change (because it has more available line width).
            // So go ahead and mark the item as dirty.
            child->setChildNeedsLayout(true, false);
        }
        
        if (childRenderBlock) {
            if (!child->avoidsFloats() && childRenderBlock->containsFloats())
                childRenderBlock->markAllDescendantsWithFloatsForLayout();
            if (!child->needsLayout())
                child->markForPaginationRelayoutIfNeeded();
        }

        // Our guess was wrong. Make the child lay itself out again.
        child->layoutIfNeeded();
    }

    // We are no longer at the top of the block if we encounter a non-empty child.  
    // This has to be done after checking for clear, so that margins can be reset if a clear occurred.
    if (marginInfo.atBeforeSideOfBlock() && !child->isSelfCollapsingBlock())
        marginInfo.setAtBeforeSideOfBlock(false);

    // Now place the child in the correct left position
    determineLogicalLeftPositionForChild(child);

    // Update our height now that the child has been placed in the correct position.
    setLogicalHeight(logicalHeight() + logicalHeightForChild(child));
    if (child->style()->marginAfterCollapse() == MSEPARATE) {
        setLogicalHeight(logicalHeight() + marginAfterForChild(child));
        marginInfo.clearMargin();
    }
    // If the child has overhanging floats that intrude into following siblings (or possibly out
    // of this block), then the parent gets notified of the floats now.
    if (childRenderBlock && childRenderBlock->containsFloats())
        maxFloatLogicalBottom = max(maxFloatLogicalBottom, addOverhangingFloats(toRenderBlock(child), !childNeededLayout));

    LayoutSize childOffset(child->x() - oldRect.x(), child->y() - oldRect.y());
    if (childOffset.width() || childOffset.height()) {
        view()->addLayoutDelta(childOffset);

        // If the child moved, we have to repaint it as well as any floating/positioned
        // descendants.  An exception is if we need a layout.  In this case, we know we're going to
        // repaint ourselves (and the child) anyway.
        if (childHadLayout && !selfNeedsLayout() && child->checkForRepaintDuringLayout())
            child->repaintDuringLayoutIfMoved(oldRect);
    }

    if (!childHadLayout && child->checkForRepaintDuringLayout()) {
        child->repaint();
        child->repaintOverhangingFloats(true);
    }

    if (paginated) {
        // Check for an after page/column break.
        LayoutUnit newHeight = applyAfterBreak(child, logicalHeight(), marginInfo);
        if (newHeight != height())
            setLogicalHeight(newHeight);
    }

    // FIXME: Change to use roughlyEquals when we move to float.
    // See https://bugs.webkit.org/show_bug.cgi?id=66148
    ASSERT(oldLayoutDelta == view()->layoutDelta());
}

void RenderBlock::simplifiedNormalFlowLayout()
{
    if (childrenInline()) {
        ListHashSet<RootInlineBox*> lineBoxes;
        for (InlineWalker walker(this); !walker.atEnd(); walker.advance()) {
            RenderObject* o = walker.current();
            if (!o->isPositioned() && (o->isReplaced() || o->isFloating())) {
                o->layoutIfNeeded();
                if (toRenderBox(o)->inlineBoxWrapper()) {
                    RootInlineBox* box = toRenderBox(o)->inlineBoxWrapper()->root();
                    lineBoxes.add(box);
                }
            } else if (o->isText() || (o->isRenderInline() && !walker.atEndOfInline()))
                o->setNeedsLayout(false);
        }

        // FIXME: Glyph overflow will get lost in this case, but not really a big deal.
        GlyphOverflowAndFallbackFontsMap textBoxDataMap;                  
        for (ListHashSet<RootInlineBox*>::const_iterator it = lineBoxes.begin(); it != lineBoxes.end(); ++it) {
            RootInlineBox* box = *it;
            box->computeOverflow(box->lineTop(), box->lineBottom(), textBoxDataMap);
        }
    } else {
        for (RenderBox* box = firstChildBox(); box; box = box->nextSiblingBox()) {
            if (!box->isPositioned())
                box->layoutIfNeeded();
        }
    }
}

bool RenderBlock::simplifiedLayout()
{
    if ((!posChildNeedsLayout() && !needsSimplifiedNormalFlowLayout()) || normalChildNeedsLayout() || selfNeedsLayout())
        return false;

    LayoutStateMaintainer statePusher(view(), this, IntSize(x(), y()), hasColumns() || hasTransform() || hasReflection() || style()->isFlippedBlocksWritingMode());
    
    if (needsPositionedMovementLayout() && !tryLayoutDoingPositionedMovementOnly())
        return false;

    // Lay out positioned descendants or objects that just need to recompute overflow.
    if (needsSimplifiedNormalFlowLayout())
        simplifiedNormalFlowLayout();

    // Lay out our positioned objects if our positioned child bit is set.
    if (posChildNeedsLayout() && layoutPositionedObjects(false))
        return false; // If a positioned float is causing our normal flow to change, then we have to bail and do a full layout.

    // Recompute our overflow information.
    // FIXME: We could do better here by computing a temporary overflow object from layoutPositionedObjects and only
    // updating our overflow if we either used to have overflow or if the new temporary object has overflow.
    // For now just always recompute overflow.  This is no worse performance-wise than the old code that called rightmostPosition and
    // lowestPosition on every relayout so it's not a regression.
    m_overflow.clear();
    computeOverflow(clientLogicalBottom(), true);

    statePusher.pop();
    
    updateLayerTransform();

    updateScrollInfoAfterLayout();

    setNeedsLayout(false);
    return true;
}

bool RenderBlock::positionedFloatsNeedRelayout()
{
    if (!hasPositionedFloats())
        return false;
    
    RenderBox* positionedObject;
    Iterator end = m_positionedObjects->end();
    for (Iterator it = m_positionedObjects->begin(); it != end; ++it) {
        positionedObject = *it;
        if (!positionedObject->isFloating())
            continue;

        if (positionedObject->needsLayout())
            return true;

        if (positionedObject->style()->hasStaticBlockPosition(isHorizontalWritingMode()) && positionedObject->parent() != this && positionedObject->parent()->isBlockFlow())
            return true;
        
        if (view()->layoutState()->pageLogicalHeightChanged() || (view()->layoutState()->pageLogicalHeight() && view()->layoutState()->pageLogicalOffset(logicalTop()) != pageLogicalOffset()))
            return true;
    }
    
    return false;
}

bool RenderBlock::layoutPositionedObjects(bool relayoutChildren)
{
    if (!m_positionedObjects)
        return false;
        
    if (hasColumns())
        view()->layoutState()->clearPaginationInformation(); // Positioned objects are not part of the column flow, so they don't paginate with the columns.

    bool didFloatingBoxRelayout = false;

    RenderBox* r;
    Iterator end = m_positionedObjects->end();
    for (Iterator it = m_positionedObjects->begin(); it != end; ++it) {
        r = *it;
        // When a non-positioned block element moves, it may have positioned children that are implicitly positioned relative to the
        // non-positioned block.  Rather than trying to detect all of these movement cases, we just always lay out positioned
        // objects that are positioned implicitly like this.  Such objects are rare, and so in typical DHTML menu usage (where everything is
        // positioned explicitly) this should not incur a performance penalty.
        if (relayoutChildren || (r->style()->hasStaticBlockPosition(isHorizontalWritingMode()) && r->parent() != this))
            r->setChildNeedsLayout(true, false);
            
        // If relayoutChildren is set and the child has percentage padding or an embedded content box, we also need to invalidate the childs pref widths.
        if (relayoutChildren && r->needsPreferredWidthsRecalculation())
            r->setPreferredLogicalWidthsDirty(true, false);
        
        if (!r->needsLayout())
            r->markForPaginationRelayoutIfNeeded();
        
        // FIXME: Technically we could check the old placement and the new placement of the box and only invalidate if
        // the margin box of the object actually changed.
        if (r->needsLayout() && r->isFloating())
            didFloatingBoxRelayout = true;

        // We don't have to do a full layout.  We just have to update our position. Try that first. If we have shrink-to-fit width
        // and we hit the available width constraint, the layoutIfNeeded() will catch it and do a full layout.
        if (r->needsPositionedMovementLayoutOnly() && r->tryLayoutDoingPositionedMovementOnly())
            r->setNeedsLayout(false);
            
        // If we are in a flow thread, go ahead and compute a vertical position for our object now.
        // If it's wrong we'll lay out again.
        LayoutUnit oldLogicalTop = 0;
        bool checkForPaginationRelayout = r->needsLayout() && view()->layoutState()->isPaginated() && view()->layoutState()->pageLogicalHeight(); 
        if (checkForPaginationRelayout) {
            if (isHorizontalWritingMode() == r->isHorizontalWritingMode())
                r->computeLogicalHeight();
            else
                r->computeLogicalWidth();
            oldLogicalTop = logicalTopForChild(r);
        }
            
        r->layoutIfNeeded();
        
        // Lay out again if our estimate was wrong.
        if (checkForPaginationRelayout && logicalTopForChild(r) != oldLogicalTop) {
            r->setChildNeedsLayout(true, false);
            r->layoutIfNeeded();
        }
    }
    
    if (hasColumns())
        view()->layoutState()->m_columnInfo = columnInfo(); // FIXME: Kind of gross. We just put this back into the layout state so that pop() will work.
        
    return didFloatingBoxRelayout;
}

void RenderBlock::markPositionedObjectsForLayout()
{
    if (m_positionedObjects) {
        RenderBox* r;
        Iterator end = m_positionedObjects->end();
        for (Iterator it = m_positionedObjects->begin(); it != end; ++it) {
            r = *it;
            r->setChildNeedsLayout(true);
        }
    }
}

void RenderBlock::markForPaginationRelayoutIfNeeded()
{
    ASSERT(!needsLayout());
    if (needsLayout())
        return;

    if (view()->layoutState()->pageLogicalHeightChanged() || (view()->layoutState()->pageLogicalHeight() && view()->layoutState()->pageLogicalOffset(logicalTop()) != pageLogicalOffset()))
        setChildNeedsLayout(true, false);
}

void RenderBlock::repaintOverhangingFloats(bool paintAllDescendants)
{
    // Repaint any overhanging floats (if we know we're the one to paint them).
    // Otherwise, bail out.
    if (!hasOverhangingFloats())
        return;

    // FIXME: Avoid disabling LayoutState. At the very least, don't disable it for floats originating
    // in this block. Better yet would be to push extra state for the containers of other floats.
    LayoutStateDisabler layoutStateDisabler(view());
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* r = *it;
        // Only repaint the object if it is overhanging, is not in its own layer, and
        // is our responsibility to paint (m_shouldPaint is set). When paintAllDescendants is true, the latter
        // condition is replaced with being a descendant of us.
        if (logicalBottomForFloat(r) > logicalHeight() && ((paintAllDescendants && r->m_renderer->isDescendantOf(this)) || r->m_shouldPaint) && !r->m_renderer->hasSelfPaintingLayer()) {
            r->m_renderer->repaint();
            r->m_renderer->repaintOverhangingFloats();
        }
    }
}
 
void RenderBlock::paint(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    LayoutPoint adjustedPaintOffset = paintOffset + location();
    
    PaintPhase phase = paintInfo.phase;

    // Check if we need to do anything at all.
    // FIXME: Could eliminate the isRoot() check if we fix background painting so that the RenderView
    // paints the root's background.
    if (!isRoot()) {
        LayoutRect overflowBox = visualOverflowRect();
        flipForWritingMode(overflowBox);
        overflowBox.inflate(maximalOutlineSize(paintInfo.phase));
        overflowBox.moveBy(adjustedPaintOffset);
        if (!overflowBox.intersects(paintInfo.rect))
            return;
    }

    bool pushedClip = pushContentsClip(paintInfo, adjustedPaintOffset);
    paintObject(paintInfo, adjustedPaintOffset);
    if (pushedClip)
        popContentsClip(paintInfo, phase, adjustedPaintOffset);

    // Our scrollbar widgets paint exactly when we tell them to, so that they work properly with
    // z-index.  We paint after we painted the background/border, so that the scrollbars will
    // sit above the background/border.
    if (hasOverflowClip() && style()->visibility() == VISIBLE && (phase == PaintPhaseBlockBackground || phase == PaintPhaseChildBlockBackground) && paintInfo.shouldPaintWithinRoot(this))
        layer()->paintOverflowControls(paintInfo.context, adjustedPaintOffset, paintInfo.rect);
}

void RenderBlock::paintColumnRules(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    if (paintInfo.context->paintingDisabled())
        return;

    const Color& ruleColor = style()->visitedDependentColor(CSSPropertyWebkitColumnRuleColor);
    bool ruleTransparent = style()->columnRuleIsTransparent();
    EBorderStyle ruleStyle = style()->columnRuleStyle();
    LayoutUnit ruleWidth = style()->columnRuleWidth();
    LayoutUnit colGap = columnGap();
    bool renderRule = ruleStyle > BHIDDEN && !ruleTransparent && ruleWidth <= colGap;
    if (!renderRule)
        return;

    // We need to do multiple passes, breaking up our child painting into strips.
    ColumnInfo* colInfo = columnInfo();
    unsigned colCount = columnCount(colInfo);
    LayoutUnit currLogicalLeftOffset = style()->isLeftToRightDirection() ? 0 : contentLogicalWidth();
    LayoutUnit ruleAdd = logicalLeftOffsetForContent();
    LayoutUnit ruleLogicalLeft = style()->isLeftToRightDirection() ? 0 : contentLogicalWidth();

    bool antialias = shouldAntialiasLines(paintInfo.context);
    LayoutUnit inlineDirectionSize = colInfo->desiredColumnWidth();

    for (unsigned i = 0; i < colCount; i++) {
        // Move to the next position.
        if (style()->isLeftToRightDirection()) {
            ruleLogicalLeft += inlineDirectionSize + colGap / 2;
            currLogicalLeftOffset += inlineDirectionSize + colGap;
        } else {
            ruleLogicalLeft -= (inlineDirectionSize + colGap / 2);
            currLogicalLeftOffset -= (inlineDirectionSize + colGap);
        }
       
        // Now paint the column rule.
        if (i < colCount - 1) {
            LayoutUnit ruleLeft = isHorizontalWritingMode() ? paintOffset.x() + ruleLogicalLeft - ruleWidth / 2 + ruleAdd : paintOffset.x() + borderLeft() + paddingLeft();
            LayoutUnit ruleRight = isHorizontalWritingMode() ? ruleLeft + ruleWidth : ruleLeft + contentWidth();
            LayoutUnit ruleTop = isHorizontalWritingMode() ? paintOffset.y() + borderTop() + paddingTop() : paintOffset.y() + ruleLogicalLeft - ruleWidth / 2 + ruleAdd;
            LayoutUnit ruleBottom = isHorizontalWritingMode() ? ruleTop + contentHeight() : ruleTop + ruleWidth;
            BoxSide side = isHorizontalWritingMode()
                ? style()->isLeftToRightDirection() ? BSLeft : BSRight
                : style()->isLeftToRightDirection() ? BSTop : BSBottom;
            drawLineForBoxSide(paintInfo.context, ruleLeft, ruleTop, ruleRight, ruleBottom, side, ruleColor, ruleStyle, 0, 0, antialias);
        }
        
        ruleLogicalLeft = currLogicalLeftOffset;
    }
}

void RenderBlock::paintColumnContents(PaintInfo& paintInfo, const LayoutPoint& paintOffset, bool paintingFloats)
{
    // We need to do multiple passes, breaking up our child painting into strips.
    GraphicsContext* context = paintInfo.context;
    ColumnInfo* colInfo = columnInfo();
    unsigned colCount = columnCount(colInfo);
    if (!colCount)
        return;
    LayoutUnit currLogicalTopOffset = 0;
    for (unsigned i = 0; i < colCount; i++) {
        // For each rect, we clip to the rect, and then we adjust our coords.
        LayoutRect colRect = columnRectAt(colInfo, i);
        flipForWritingMode(colRect);
        LayoutUnit logicalLeftOffset = (isHorizontalWritingMode() ? colRect.x() : colRect.y()) - logicalLeftOffsetForContent();
        LayoutSize offset = isHorizontalWritingMode() ? LayoutSize(logicalLeftOffset, currLogicalTopOffset) : LayoutSize(currLogicalTopOffset, logicalLeftOffset);
        colRect.moveBy(paintOffset);
        PaintInfo info(paintInfo);
        info.rect.intersect(colRect);
        
        if (!info.rect.isEmpty()) {
            GraphicsContextStateSaver stateSaver(*context);
            
            // Each strip pushes a clip, since column boxes are specified as being
            // like overflow:hidden.
            context->clip(colRect);

            // Adjust our x and y when painting.
            LayoutPoint adjustedPaintOffset = paintOffset + offset;
            if (paintingFloats)
                paintFloats(info, adjustedPaintOffset, paintInfo.phase == PaintPhaseSelection || paintInfo.phase == PaintPhaseTextClip);
            else
                paintContents(info, adjustedPaintOffset);
        }

        LayoutUnit blockDelta = (isHorizontalWritingMode() ? colRect.height() : colRect.width());
        if (style()->isFlippedBlocksWritingMode())
            currLogicalTopOffset += blockDelta;
        else
            currLogicalTopOffset -= blockDelta;
    }
}

void RenderBlock::paintContents(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    // Avoid painting descendants of the root element when stylesheets haven't loaded.  This eliminates FOUC.
    // It's ok not to draw, because later on, when all the stylesheets do load, updateStyleSelector on the Document
    // will do a full repaint().
    if (document()->didLayoutWithPendingStylesheets() && !isRenderView())
        return;

    if (childrenInline())
        m_lineBoxes.paint(this, paintInfo, paintOffset);
    else
        paintChildren(paintInfo, paintOffset);
}

void RenderBlock::paintChildren(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    PaintPhase newPhase = (paintInfo.phase == PaintPhaseChildOutlines) ? PaintPhaseOutline : paintInfo.phase;
    newPhase = (newPhase == PaintPhaseChildBlockBackgrounds) ? PaintPhaseChildBlockBackground : newPhase;
    
    // We don't paint our own background, but we do let the kids paint their backgrounds.
    PaintInfo info(paintInfo);
    info.phase = newPhase;
    info.updatePaintingRootForChildren(this);
    
    // FIXME: Paint-time pagination is obsolete and is now only used by embedded WebViews inside AppKit
    // NSViews.  Do not add any more code for this.
    RenderView* renderView = view();
    bool usePrintRect = !renderView->printRect().isEmpty();
    
    for (RenderBox* child = firstChildBox(); child; child = child->nextSiblingBox()) {        
        // Check for page-break-before: always, and if it's set, break and bail.
        bool checkBeforeAlways = !childrenInline() && (usePrintRect && child->style()->pageBreakBefore() == PBALWAYS);
        LayoutUnit absoluteChildY = paintOffset.y() + child->y();
        if (checkBeforeAlways
            && absoluteChildY > paintInfo.rect.y()
            && absoluteChildY < paintInfo.rect.maxY()) {
            view()->setBestTruncatedAt(absoluteChildY, this, true);
            return;
        }

        if (!child->isFloating() && child->isReplaced() && usePrintRect && child->height() <= renderView->printRect().height()) {
            // Paginate block-level replaced elements.
            if (absoluteChildY + child->height() > renderView->printRect().maxY()) {
                if (absoluteChildY < renderView->truncatedAt())
                    renderView->setBestTruncatedAt(absoluteChildY, child);
                // If we were able to truncate, don't paint.
                if (absoluteChildY >= renderView->truncatedAt())
                    break;
            }
        }

        LayoutPoint childPoint = flipForWritingModeForChild(child, paintOffset);
        if (!child->hasSelfPaintingLayer() && !child->isFloating())
            child->paint(info, childPoint);

        // Check for page-break-after: always, and if it's set, break and bail.
        bool checkAfterAlways = !childrenInline() && (usePrintRect && child->style()->pageBreakAfter() == PBALWAYS);
        if (checkAfterAlways
            && (absoluteChildY + child->height()) > paintInfo.rect.y()
            && (absoluteChildY + child->height()) < paintInfo.rect.maxY()) {
            view()->setBestTruncatedAt(absoluteChildY + child->height() + max<LayoutUnit>(0, child->collapsedMarginAfter()), this, true);
            return;
        }
    }
}

void RenderBlock::paintCaret(PaintInfo& paintInfo, const LayoutPoint& paintOffset, CaretType type)
{
    // Paint the caret if the FrameSelection says so or if caret browsing is enabled
    bool caretBrowsing = frame()->settings() && frame()->settings()->caretBrowsingEnabled();
    RenderObject* caretPainter;
    bool isContentEditable;
    if (type == CursorCaret) {
        caretPainter = frame()->selection()->caretRenderer();
        isContentEditable = frame()->selection()->isContentEditable();
    } else {
        caretPainter = frame()->page()->dragCaretController()->caretRenderer();
        isContentEditable = frame()->page()->dragCaretController()->isContentEditable();
    }

    if (caretPainter == this && (isContentEditable || caretBrowsing)) {
        // Convert the painting offset into the local coordinate system of this renderer,
        // to match the localCaretRect computed by the FrameSelection
        LayoutPoint adjustedPaintOffset = paintOffset;
        offsetForContents(adjustedPaintOffset);

        if (type == CursorCaret)
            frame()->selection()->paintCaret(paintInfo.context, adjustedPaintOffset, paintInfo.rect);
        else
            frame()->page()->dragCaretController()->paintDragCaret(frame(), paintInfo.context, adjustedPaintOffset, paintInfo.rect);
    }
}

void RenderBlock::paintObject(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    PaintPhase paintPhase = paintInfo.phase;

    // 1. paint background, borders etc
    if ((paintPhase == PaintPhaseBlockBackground || paintPhase == PaintPhaseChildBlockBackground) && style()->visibility() == VISIBLE) {
        if (hasBoxDecorations())
            paintBoxDecorations(paintInfo, paintOffset);
        if (hasColumns())
            paintColumnRules(paintInfo, paintOffset);
    }

    if (paintPhase == PaintPhaseMask && style()->visibility() == VISIBLE) {
        paintMask(paintInfo, paintOffset);
        return;
    }

    // We're done.  We don't bother painting any children.
    if (paintPhase == PaintPhaseBlockBackground)
        return;

    // Adjust our painting position if we're inside a scrolled layer (e.g., an overflow:auto div).
    LayoutPoint scrolledOffset = paintOffset;
    if (hasOverflowClip())
        scrolledOffset.move(-layer()->scrolledContentOffset());

    // 2. paint contents
    if (paintPhase != PaintPhaseSelfOutline) {
        if (hasColumns())
            paintColumnContents(paintInfo, scrolledOffset);
        else
            paintContents(paintInfo, scrolledOffset);
    }

    // 3. paint selection
    // FIXME: Make this work with multi column layouts.  For now don't fill gaps.
    bool isPrinting = document()->printing();
    if (!isPrinting && !hasColumns())
        paintSelection(paintInfo, scrolledOffset); // Fill in gaps in selection on lines and between blocks.

    // 4. paint floats.
    if (paintPhase == PaintPhaseFloat || paintPhase == PaintPhaseSelection || paintPhase == PaintPhaseTextClip) {
        if (hasColumns())
            paintColumnContents(paintInfo, scrolledOffset, true);
        else
            paintFloats(paintInfo, scrolledOffset, paintPhase == PaintPhaseSelection || paintPhase == PaintPhaseTextClip);
    }

    // 5. paint outline.
    if ((paintPhase == PaintPhaseOutline || paintPhase == PaintPhaseSelfOutline) && hasOutline() && style()->visibility() == VISIBLE)
        paintOutline(paintInfo.context, LayoutRect(paintOffset, size()));

    // 6. paint continuation outlines.
    if ((paintPhase == PaintPhaseOutline || paintPhase == PaintPhaseChildOutlines)) {
        RenderInline* inlineCont = inlineElementContinuation();
        if (inlineCont && inlineCont->hasOutline() && inlineCont->style()->visibility() == VISIBLE) {
            RenderInline* inlineRenderer = toRenderInline(inlineCont->node()->renderer());
            RenderBlock* cb = containingBlock();

            bool inlineEnclosedInSelfPaintingLayer = false;
            for (RenderBoxModelObject* box = inlineRenderer; box != cb; box = box->parent()->enclosingBoxModelObject()) {
                if (box->hasSelfPaintingLayer()) {
                    inlineEnclosedInSelfPaintingLayer = true;
                    break;
                }
            }

            if (!inlineEnclosedInSelfPaintingLayer)
                cb->addContinuationWithOutline(inlineRenderer);
            else if (!inlineRenderer->firstLineBox())
                inlineRenderer->paintOutline(paintInfo.context, paintOffset - locationOffset() + inlineRenderer->containingBlock()->location());
        }
        paintContinuationOutlines(paintInfo, paintOffset);
    }

    // 7. paint caret.
    // If the caret's node's render object's containing block is this block, and the paint action is PaintPhaseForeground,
    // then paint the caret.
    if (paintPhase == PaintPhaseForeground) {        
        paintCaret(paintInfo, scrolledOffset, CursorCaret);
        paintCaret(paintInfo, scrolledOffset, DragCaret);
    }
}

LayoutPoint RenderBlock::flipFloatForWritingModeForChild(const FloatingObject* child, const LayoutPoint& point) const
{
    if (!style()->isFlippedBlocksWritingMode())
        return point;
    
    // This is similar to RenderBox::flipForWritingModeForChild. We have to subtract out our left/top offsets twice, since
    // it's going to get added back in. We hide this complication here so that the calling code looks normal for the unflipped
    // case.
    if (isHorizontalWritingMode())
        return LayoutPoint(point.x(), point.y() + height() - child->renderer()->height() - 2 * yPositionForFloatIncludingMargin(child));
    return LayoutPoint(point.x() + width() - child->width() - 2 * xPositionForFloatIncludingMargin(child), point.y());
}

void RenderBlock::paintFloats(PaintInfo& paintInfo, const LayoutPoint& paintOffset, bool preservePhase)
{
    if (!m_floatingObjects)
        return;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* r = *it;
        // Only paint the object if our m_shouldPaint flag is set.
        if (r->m_shouldPaint && !r->m_renderer->hasSelfPaintingLayer()) {
            PaintInfo currentPaintInfo(paintInfo);
            currentPaintInfo.phase = preservePhase ? paintInfo.phase : PaintPhaseBlockBackground;
            LayoutPoint childPoint = flipFloatForWritingModeForChild(r, LayoutPoint(paintOffset.x() + xPositionForFloatIncludingMargin(r) - r->m_renderer->x(), paintOffset.y() + yPositionForFloatIncludingMargin(r) - r->m_renderer->y()));
            r->m_renderer->paint(currentPaintInfo, childPoint);
            if (!preservePhase) {
                currentPaintInfo.phase = PaintPhaseChildBlockBackgrounds;
                r->m_renderer->paint(currentPaintInfo, childPoint);
                currentPaintInfo.phase = PaintPhaseFloat;
                r->m_renderer->paint(currentPaintInfo, childPoint);
                currentPaintInfo.phase = PaintPhaseForeground;
                r->m_renderer->paint(currentPaintInfo, childPoint);
                currentPaintInfo.phase = PaintPhaseOutline;
                r->m_renderer->paint(currentPaintInfo, childPoint);
            }
        }
    }
}

void RenderBlock::paintEllipsisBoxes(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    if (!paintInfo.shouldPaintWithinRoot(this) || !firstLineBox())
        return;

    if (style()->visibility() == VISIBLE && paintInfo.phase == PaintPhaseForeground) {
        // We can check the first box and last box and avoid painting if we don't
        // intersect.
        LayoutUnit yPos = paintOffset.y() + firstLineBox()->y();
        LayoutUnit h = lastLineBox()->y() + lastLineBox()->logicalHeight() - firstLineBox()->y();
        if (yPos >= paintInfo.rect.maxY() || yPos + h <= paintInfo.rect.y())
            return;

        // See if our boxes intersect with the dirty rect.  If so, then we paint
        // them.  Note that boxes can easily overlap, so we can't make any assumptions
        // based off positions of our first line box or our last line box.
        for (RootInlineBox* curr = firstRootBox(); curr; curr = curr->nextRootBox()) {
            yPos = paintOffset.y() + curr->y();
            h = curr->logicalHeight();
            if (curr->ellipsisBox() && yPos < paintInfo.rect.maxY() && yPos + h > paintInfo.rect.y())
                curr->paintEllipsisBox(paintInfo, paintOffset, curr->lineTop(), curr->lineBottom());
        }
    }
}

RenderInline* RenderBlock::inlineElementContinuation() const
{ 
    RenderBoxModelObject* continuation = this->continuation();
    return continuation && continuation->isInline() ? toRenderInline(continuation) : 0;
}

RenderBlock* RenderBlock::blockElementContinuation() const
{
    RenderBoxModelObject* currentContinuation = continuation();
    if (!currentContinuation || currentContinuation->isInline())
        return 0;
    RenderBlock* nextContinuation = toRenderBlock(currentContinuation);
    if (nextContinuation->isAnonymousBlock())
        return nextContinuation->blockElementContinuation();
    return nextContinuation;
}
    
static ContinuationOutlineTableMap* continuationOutlineTable()
{
    DEFINE_STATIC_LOCAL(ContinuationOutlineTableMap, table, ());
    return &table;
}

void RenderBlock::addContinuationWithOutline(RenderInline* flow)
{
    // We can't make this work if the inline is in a layer.  We'll just rely on the broken
    // way of painting.
    ASSERT(!flow->layer() && !flow->isInlineElementContinuation());
    
    ContinuationOutlineTableMap* table = continuationOutlineTable();
    ListHashSet<RenderInline*>* continuations = table->get(this);
    if (!continuations) {
        continuations = new ListHashSet<RenderInline*>;
        table->set(this, continuations);
    }
    
    continuations->add(flow);
}

bool RenderBlock::paintsContinuationOutline(RenderInline* flow)
{
    ContinuationOutlineTableMap* table = continuationOutlineTable();
    if (table->isEmpty())
        return false;
        
    ListHashSet<RenderInline*>* continuations = table->get(this);
    if (!continuations)
        return false;

    return continuations->contains(flow);
}

void RenderBlock::paintContinuationOutlines(PaintInfo& info, const LayoutPoint& paintOffset)
{
    ContinuationOutlineTableMap* table = continuationOutlineTable();
    if (table->isEmpty())
        return;
        
    ListHashSet<RenderInline*>* continuations = table->get(this);
    if (!continuations)
        return;

    LayoutPoint accumulatedPaintOffset = paintOffset;
    // Paint each continuation outline.
    ListHashSet<RenderInline*>::iterator end = continuations->end();
    for (ListHashSet<RenderInline*>::iterator it = continuations->begin(); it != end; ++it) {
        // Need to add in the coordinates of the intervening blocks.
        RenderInline* flow = *it;
        RenderBlock* block = flow->containingBlock();
        for ( ; block && block != this; block = block->containingBlock())
            accumulatedPaintOffset.moveBy(block->location());
        ASSERT(block);   
        flow->paintOutline(info.context, accumulatedPaintOffset);
    }
    
    // Delete
    delete continuations;
    table->remove(this);
}

bool RenderBlock::shouldPaintSelectionGaps() const
{
    return selectionState() != SelectionNone && style()->visibility() == VISIBLE && isSelectionRoot();
}

bool RenderBlock::isSelectionRoot() const
{
    if (!node())
        return false;
        
    // FIXME: Eventually tables should have to learn how to fill gaps between cells, at least in simple non-spanning cases.
    if (isTable())
        return false;
        
    if (isBody() || isRoot() || hasOverflowClip() || isRelPositioned() ||
        isFloatingOrPositioned() || isTableCell() || isInlineBlockOrInlineTable() || hasTransform() ||
        hasReflection() || hasMask() || isWritingModeRoot())
        return true;
    
    if (view() && view()->selectionStart()) {
        Node* startElement = view()->selectionStart()->node();
        if (startElement && startElement->rootEditableElement() == node())
            return true;
    }
    
    return false;
}

GapRects RenderBlock::selectionGapRectsForRepaint(RenderBoxModelObject* repaintContainer)
{
    ASSERT(!needsLayout());

    if (!shouldPaintSelectionGaps())
        return GapRects();

    // FIXME: this is broken with transforms
    TransformState transformState(TransformState::ApplyTransformDirection, FloatPoint());
    mapLocalToContainer(repaintContainer, false, false, transformState);
    LayoutPoint offsetFromRepaintContainer = roundedLayoutPoint(transformState.mappedPoint());

    if (hasOverflowClip())
        offsetFromRepaintContainer -= layer()->scrolledContentOffset();

    LayoutUnit lastTop = 0;
    LayoutUnit lastLeft = logicalLeftSelectionOffset(this, lastTop);
    LayoutUnit lastRight = logicalRightSelectionOffset(this, lastTop);
    
    return selectionGaps(this, offsetFromRepaintContainer, IntSize(), lastTop, lastLeft, lastRight);
}

void RenderBlock::paintSelection(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
{
    if (shouldPaintSelectionGaps() && paintInfo.phase == PaintPhaseForeground) {
        LayoutUnit lastTop = 0;
        LayoutUnit lastLeft = logicalLeftSelectionOffset(this, lastTop);
        LayoutUnit lastRight = logicalRightSelectionOffset(this, lastTop);
        GraphicsContextStateSaver stateSaver(*paintInfo.context);

        LayoutRect gapRectsBounds = selectionGaps(this, paintOffset, LayoutSize(), lastTop, lastLeft, lastRight, &paintInfo);
        if (!gapRectsBounds.isEmpty()) {
            if (RenderLayer* layer = enclosingLayer()) {
                gapRectsBounds.moveBy(-paintOffset);
                if (!hasLayer()) {
                    LayoutRect localBounds(gapRectsBounds);
                    flipForWritingMode(localBounds);
                    gapRectsBounds = localToContainerQuad(FloatRect(localBounds), layer->renderer()).enclosingBoundingBox();
                    gapRectsBounds.move(layer->scrolledContentOffset());
                }
                layer->addBlockSelectionGapsBounds(gapRectsBounds);
            }
        }
    }
}

static void clipOutPositionedObjects(const PaintInfo* paintInfo, const LayoutPoint& offset, RenderBlock::PositionedObjectsListHashSet* positionedObjects)
{
    if (!positionedObjects)
        return;
    
    RenderBlock::PositionedObjectsListHashSet::const_iterator end = positionedObjects->end();
    for (RenderBlock::PositionedObjectsListHashSet::const_iterator it = positionedObjects->begin(); it != end; ++it) {
        RenderBox* r = *it;
        paintInfo->context->clipOut(LayoutRect(offset.x() + r->x(), offset.y() + r->y(), r->width(), r->height()));
    }
}

static int blockDirectionOffset(RenderBlock* rootBlock, const LayoutSize& offsetFromRootBlock)
{
    return rootBlock->isHorizontalWritingMode() ? offsetFromRootBlock.height() : offsetFromRootBlock.width();
}

static int inlineDirectionOffset(RenderBlock* rootBlock, const LayoutSize& offsetFromRootBlock)
{
    return rootBlock->isHorizontalWritingMode() ? offsetFromRootBlock.width() : offsetFromRootBlock.height();
}

LayoutRect RenderBlock::logicalRectToPhysicalRect(const LayoutPoint& rootBlockPhysicalPosition, const LayoutRect& logicalRect)
{
    LayoutRect result;
    if (isHorizontalWritingMode())
        result = logicalRect;
    else
        result = LayoutRect(logicalRect.y(), logicalRect.x(), logicalRect.height(), logicalRect.width());
    flipForWritingMode(result);
    result.moveBy(rootBlockPhysicalPosition);
    return result;
}

GapRects RenderBlock::selectionGaps(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                    LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo* paintInfo)
{
    // IMPORTANT: Callers of this method that intend for painting to happen need to do a save/restore.
    // Clip out floating and positioned objects when painting selection gaps.
    if (paintInfo) {
        // Note that we don't clip out overflow for positioned objects.  We just stick to the border box.
        LayoutRect flippedBlockRect(offsetFromRootBlock.width(), offsetFromRootBlock.height(), width(), height());
        rootBlock->flipForWritingMode(flippedBlockRect);
        flippedBlockRect.moveBy(rootBlockPhysicalPosition);
        clipOutPositionedObjects(paintInfo, flippedBlockRect.location(), m_positionedObjects.get());
        if (isBody() || isRoot()) // The <body> must make sure to examine its containingBlock's positioned objects.
            for (RenderBlock* cb = containingBlock(); cb && !cb->isRenderView(); cb = cb->containingBlock())
                clipOutPositionedObjects(paintInfo, LayoutPoint(cb->x(), cb->y()), cb->m_positionedObjects.get()); // FIXME: Not right for flipped writing modes.
        if (m_floatingObjects) {
            const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
            FloatingObjectSetIterator end = floatingObjectSet.end();
            for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                FloatingObject* r = *it;
                LayoutRect floatBox(offsetFromRootBlock.width() + xPositionForFloatIncludingMargin(r),
                                    offsetFromRootBlock.height() + yPositionForFloatIncludingMargin(r),
                                    r->m_renderer->width(), r->m_renderer->height());
                rootBlock->flipForWritingMode(floatBox);
                floatBox.move(rootBlockPhysicalPosition.x(), rootBlockPhysicalPosition.y());
                paintInfo->context->clipOut(floatBox);
            }
        }
    }

    // FIXME: overflow: auto/scroll regions need more math here, since painting in the border box is different from painting in the padding box (one is scrolled, the other is
    // fixed).
    GapRects result;
    if (!isBlockFlow()) // FIXME: Make multi-column selection gap filling work someday.
        return result;

    if (hasColumns() || hasTransform() || style()->columnSpan()) {
        // FIXME: We should learn how to gap fill multiple columns and transforms eventually.
        lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalHeight();
        lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, logicalHeight());
        lastLogicalRight = logicalRightSelectionOffset(rootBlock, logicalHeight());
        return result;
    }

    if (childrenInline())
        result = inlineSelectionGaps(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, paintInfo);
    else
        result = blockSelectionGaps(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, paintInfo);

    // Go ahead and fill the vertical gap all the way to the bottom of our block if the selection extends past our block.
    if (rootBlock == this && (selectionState() != SelectionBoth && selectionState() != SelectionEnd))
        result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, 
                                             logicalHeight(), paintInfo));
    return result;
}

GapRects RenderBlock::inlineSelectionGaps(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                          LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo* paintInfo)
{
    GapRects result;

    bool containsStart = selectionState() == SelectionStart || selectionState() == SelectionBoth;

    if (!firstLineBox()) {
        if (containsStart) {
            // Go ahead and update our lastLogicalTop to be the bottom of the block.  <hr>s or empty blocks with height can trip this
            // case.
            lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalHeight();
            lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, logicalHeight());
            lastLogicalRight = logicalRightSelectionOffset(rootBlock, logicalHeight());
        }
        return result;
    }

    RootInlineBox* lastSelectedLine = 0;
    RootInlineBox* curr;
    for (curr = firstRootBox(); curr && !curr->hasSelectedChildren(); curr = curr->nextRootBox()) { }

    // Now paint the gaps for the lines.
    for (; curr && curr->hasSelectedChildren(); curr = curr->nextRootBox()) {
        LayoutUnit selTop =  curr->selectionTop();
        LayoutUnit selHeight = curr->selectionHeight();

        if (!containsStart && !lastSelectedLine &&
            selectionState() != SelectionStart && selectionState() != SelectionBoth)
            result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, 
                                                 selTop, paintInfo));
        
        LayoutRect logicalRect(curr->logicalLeft(), selTop, curr->logicalWidth(), selTop + selHeight);
        logicalRect.move(isHorizontalWritingMode() ? offsetFromRootBlock : offsetFromRootBlock.transposedSize());
        LayoutRect physicalRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, logicalRect);
        if (!paintInfo || (isHorizontalWritingMode() && physicalRect.y() < paintInfo->rect.maxY() && physicalRect.maxY() > paintInfo->rect.y())
            || (!isHorizontalWritingMode() && physicalRect.x() < paintInfo->rect.maxX() && physicalRect.maxX() > paintInfo->rect.x()))
            result.unite(curr->lineSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, selTop, selHeight, paintInfo));

        lastSelectedLine = curr;
    }

    if (containsStart && !lastSelectedLine)
        // VisibleSelection must start just after our last line.
        lastSelectedLine = lastRootBox();

    if (lastSelectedLine && selectionState() != SelectionEnd && selectionState() != SelectionBoth) {
        // Go ahead and update our lastY to be the bottom of the last selected line.
        lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + lastSelectedLine->selectionBottom();
        lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
        lastLogicalRight = logicalRightSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
    }
    return result;
}

GapRects RenderBlock::blockSelectionGaps(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                         LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo* paintInfo)
{
    GapRects result;

    // Go ahead and jump right to the first block child that contains some selected objects.
    RenderBox* curr;
    for (curr = firstChildBox(); curr && curr->selectionState() == SelectionNone; curr = curr->nextSiblingBox()) { }

    for (bool sawSelectionEnd = false; curr && !sawSelectionEnd; curr = curr->nextSiblingBox()) {
        SelectionState childState = curr->selectionState();
        if (childState == SelectionBoth || childState == SelectionEnd)
            sawSelectionEnd = true;

        if (curr->isFloatingOrPositioned())
            continue; // We must be a normal flow object in order to even be considered.

        if (curr->isRelPositioned() && curr->hasLayer()) {
            // If the relposition offset is anything other than 0, then treat this just like an absolute positioned element.
            // Just disregard it completely.
            LayoutSize relOffset = curr->layer()->relativePositionOffset();
            if (relOffset.width() || relOffset.height())
                continue;
        }

        bool paintsOwnSelection = curr->shouldPaintSelectionGaps() || curr->isTable(); // FIXME: Eventually we won't special-case table like this.
        bool fillBlockGaps = paintsOwnSelection || (curr->canBeSelectionLeaf() && childState != SelectionNone);
        if (fillBlockGaps) {
            // We need to fill the vertical gap above this object.
            if (childState == SelectionEnd || childState == SelectionInside)
                // Fill the gap above the object.
                result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, 
                                                     curr->logicalTop(), paintInfo));

            // Only fill side gaps for objects that paint their own selection if we know for sure the selection is going to extend all the way *past*
            // our object.  We know this if the selection did not end inside our object.
            if (paintsOwnSelection && (childState == SelectionStart || sawSelectionEnd))
                childState = SelectionNone;

            // Fill side gaps on this object based off its state.
            bool leftGap, rightGap;
            getSelectionGapInfo(childState, leftGap, rightGap);

            if (leftGap)
                result.uniteLeft(logicalLeftSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, this, curr->logicalLeft(), curr->logicalTop(), curr->logicalHeight(), paintInfo));
            if (rightGap)
                result.uniteRight(logicalRightSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, this, curr->logicalRight(), curr->logicalTop(), curr->logicalHeight(), paintInfo));

            // Update lastLogicalTop to be just underneath the object.  lastLogicalLeft and lastLogicalRight extend as far as
            // they can without bumping into floating or positioned objects.  Ideally they will go right up
            // to the border of the root selection block.
            lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + curr->logicalBottom();
            lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, curr->logicalBottom());
            lastLogicalRight = logicalRightSelectionOffset(rootBlock, curr->logicalBottom());
        } else if (childState != SelectionNone)
            // We must be a block that has some selected object inside it.  Go ahead and recur.
            result.unite(toRenderBlock(curr)->selectionGaps(rootBlock, rootBlockPhysicalPosition, LayoutSize(offsetFromRootBlock.width() + curr->x(), offsetFromRootBlock.height() + curr->y()), 
                                                            lastLogicalTop, lastLogicalLeft, lastLogicalRight, paintInfo));
    }
    return result;
}

LayoutRect RenderBlock::blockSelectionGap(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                          LayoutUnit lastLogicalTop, LayoutUnit lastLogicalLeft, LayoutUnit lastLogicalRight, LayoutUnit logicalBottom, const PaintInfo* paintInfo)
{
    LayoutUnit logicalTop = lastLogicalTop;
    LayoutUnit logicalHeight = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalBottom - logicalTop;
    if (logicalHeight <= static_cast<LayoutUnit>(0))
        return LayoutRect();

    // Get the selection offsets for the bottom of the gap
    LayoutUnit logicalLeft = max(lastLogicalLeft, logicalLeftSelectionOffset(rootBlock, logicalBottom));
    LayoutUnit logicalRight = min(lastLogicalRight, logicalRightSelectionOffset(rootBlock, logicalBottom));
    LayoutUnit logicalWidth = logicalRight - logicalLeft;
    if (logicalWidth <= static_cast<LayoutUnit>(0))
        return LayoutRect();

    LayoutRect gapRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, LayoutRect(logicalLeft, logicalTop, logicalWidth, logicalHeight));
    if (paintInfo)
        paintInfo->context->fillRect(gapRect, selectionBackgroundColor(), style()->colorSpace());
    return gapRect;
}

LayoutRect RenderBlock::logicalLeftSelectionGap(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                                RenderObject* selObj, LayoutUnit logicalLeft, LayoutUnit logicalTop, LayoutUnit logicalHeight, const PaintInfo* paintInfo)
{
    LayoutUnit rootBlockLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalTop;
    LayoutUnit rootBlockLogicalLeft = max(logicalLeftSelectionOffset(rootBlock, logicalTop), logicalLeftSelectionOffset(rootBlock, logicalTop + logicalHeight));
    LayoutUnit rootBlockLogicalRight = min(inlineDirectionOffset(rootBlock, offsetFromRootBlock) + logicalLeft, min(logicalRightSelectionOffset(rootBlock, logicalTop), logicalRightSelectionOffset(rootBlock, logicalTop + logicalHeight)));
    LayoutUnit rootBlockLogicalWidth = rootBlockLogicalRight - rootBlockLogicalLeft;
    if (rootBlockLogicalWidth <= static_cast<LayoutUnit>(0))
        return LayoutRect();

    LayoutRect gapRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, LayoutRect(rootBlockLogicalLeft, rootBlockLogicalTop, rootBlockLogicalWidth, logicalHeight));
    if (paintInfo)
        paintInfo->context->fillRect(gapRect, selObj->selectionBackgroundColor(), selObj->style()->colorSpace());
    return gapRect;
}

LayoutRect RenderBlock::logicalRightSelectionGap(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
                                                 RenderObject* selObj, LayoutUnit logicalRight, LayoutUnit logicalTop, LayoutUnit logicalHeight, const PaintInfo* paintInfo)
{
    LayoutUnit rootBlockLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalTop;
    LayoutUnit rootBlockLogicalLeft = max(inlineDirectionOffset(rootBlock, offsetFromRootBlock) + logicalRight, max(logicalLeftSelectionOffset(rootBlock, logicalTop), logicalLeftSelectionOffset(rootBlock, logicalTop + logicalHeight)));
    LayoutUnit rootBlockLogicalRight = min(logicalRightSelectionOffset(rootBlock, logicalTop), logicalRightSelectionOffset(rootBlock, logicalTop + logicalHeight));
    LayoutUnit rootBlockLogicalWidth = rootBlockLogicalRight - rootBlockLogicalLeft;
    if (rootBlockLogicalWidth <= static_cast<LayoutUnit>(0))
        return LayoutRect();

    LayoutRect gapRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, LayoutRect(rootBlockLogicalLeft, rootBlockLogicalTop, rootBlockLogicalWidth, logicalHeight));
    if (paintInfo)
        paintInfo->context->fillRect(gapRect, selObj->selectionBackgroundColor(), selObj->style()->colorSpace());
    return gapRect;
}

void RenderBlock::getSelectionGapInfo(SelectionState state, bool& leftGap, bool& rightGap)
{
    bool ltr = style()->isLeftToRightDirection();
    leftGap = (state == RenderObject::SelectionInside) ||
              (state == RenderObject::SelectionEnd && ltr) ||
              (state == RenderObject::SelectionStart && !ltr);
    rightGap = (state == RenderObject::SelectionInside) ||
               (state == RenderObject::SelectionStart && ltr) ||
               (state == RenderObject::SelectionEnd && !ltr);
}

LayoutUnit RenderBlock::logicalLeftSelectionOffset(RenderBlock* rootBlock, LayoutUnit position)
{
    LayoutUnit logicalLeft = logicalLeftOffsetForLine(position, false);
    if (logicalLeft == logicalLeftOffsetForContent()) {
        if (rootBlock != this)
            // The border can potentially be further extended by our containingBlock().
            return containingBlock()->logicalLeftSelectionOffset(rootBlock, position + logicalTop());
        return logicalLeft;
    } else {
        RenderBlock* cb = this;
        while (cb != rootBlock) {
            logicalLeft += cb->logicalLeft();
            cb = cb->containingBlock();
        }
    }
    return logicalLeft;
}

LayoutUnit RenderBlock::logicalRightSelectionOffset(RenderBlock* rootBlock, LayoutUnit position)
{
    LayoutUnit logicalRight = logicalRightOffsetForLine(position, false);
    if (logicalRight == logicalRightOffsetForContent()) {
        if (rootBlock != this)
            // The border can potentially be further extended by our containingBlock().
            return containingBlock()->logicalRightSelectionOffset(rootBlock, position + logicalTop());
        return logicalRight;
    } else {
        RenderBlock* cb = this;
        while (cb != rootBlock) {
            logicalRight += cb->logicalLeft();
            cb = cb->containingBlock();
        }
    }
    return logicalRight;
}

void RenderBlock::insertPositionedObject(RenderBox* o)
{
    if (o->isRenderFlowThread())
        return;
    
    // Create the list of special objects if we don't aleady have one
    if (!m_positionedObjects)
        m_positionedObjects = adoptPtr(new PositionedObjectsListHashSet);

    m_positionedObjects->add(o);
}

void RenderBlock::removePositionedObject(RenderBox* o)
{
    if (m_positionedObjects)
        m_positionedObjects->remove(o);
}

void RenderBlock::removePositionedObjects(RenderBlock* o)
{
    if (!m_positionedObjects)
        return;
    
    RenderBox* r;
    
    Iterator end = m_positionedObjects->end();
    
    Vector<RenderBox*, 16> deadObjects;

    for (Iterator it = m_positionedObjects->begin(); it != end; ++it) {
        r = *it;
        if (!o || r->isDescendantOf(o)) {
            if (o)
                r->setChildNeedsLayout(true, false);
            
            // It is parent blocks job to add positioned child to positioned objects list of its containing block
            // Parent layout needs to be invalidated to ensure this happens.
            RenderObject* p = r->parent();
            while (p && !p->isRenderBlock())
                p = p->parent();
            if (p)
                p->setChildNeedsLayout(true);
            
            deadObjects.append(r);
        }
    }
    
    for (unsigned i = 0; i < deadObjects.size(); i++)
        m_positionedObjects->remove(deadObjects.at(i));
}

RenderBlock::FloatingObject* RenderBlock::insertFloatingObject(RenderBox* o)
{
    ASSERT(o->isFloating());

    // Create the list of special objects if we don't aleady have one
    if (!m_floatingObjects)
        m_floatingObjects = adoptPtr(new FloatingObjects(isHorizontalWritingMode()));
    else {
        // Don't insert the object again if it's already in the list
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator it = floatingObjectSet.find<RenderBox*, FloatingObjectHashTranslator>(o);
        if (it != floatingObjectSet.end())
            return *it;
    }

    // Create the special object entry & append it to the list

    FloatingObject* newObj = new FloatingObject(o->style()->floating());
    
    // Our location is irrelevant if we're unsplittable or no pagination is in effect.
    // Just go ahead and lay out the float.
    if (!o->isPositioned()) {
        bool isChildRenderBlock = o->isRenderBlock();
        if (isChildRenderBlock && !o->needsLayout() && view()->layoutState()->pageLogicalHeightChanged())
            o->setChildNeedsLayout(true, false);
            
        bool affectedByPagination = isChildRenderBlock && view()->layoutState()->m_pageLogicalHeight;
        if (!affectedByPagination || isWritingModeRoot()) // We are unsplittable if we're a block flow root.
            o->layoutIfNeeded();
        else {
            o->computeLogicalWidth();
            o->computeBlockDirectionMargins(this);
        }
    }
    setLogicalWidthForFloat(newObj, logicalWidthForChild(o) + marginStartForChild(o) + marginEndForChild(o));

    newObj->m_shouldPaint = !o->hasSelfPaintingLayer(); // If a layer exists, the float will paint itself.  Otherwise someone else will.
    newObj->m_isDescendant = true;
    newObj->m_renderer = o;

    m_floatingObjects->add(newObj);
    
    return newObj;
}

void RenderBlock::removeFloatingObject(RenderBox* o)
{
    if (m_floatingObjects) {
        const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
        FloatingObjectSetIterator it = floatingObjectSet.find<RenderBox*, FloatingObjectHashTranslator>(o);
        if (it != floatingObjectSet.end()) {
            FloatingObject* r = *it;
            if (childrenInline()) {
                int logicalTop = logicalTopForFloat(r);
                int logicalBottom = logicalBottomForFloat(r);

                // Fix for https://bugs.webkit.org/show_bug.cgi?id=54995.
                if (logicalBottom < 0 || logicalBottom < logicalTop || logicalTop == numeric_limits<int>::max())
                    logicalBottom = numeric_limits<int>::max();
                else {
                    // Special-case zero- and less-than-zero-height floats: those don't touch
                    // the line that they're on, but it still needs to be dirtied. This is
                    // accomplished by pretending they have a height of 1.
                    logicalBottom = max(logicalBottom, logicalTop + 1);
                }
                if (r->m_originatingLine) {
                    if (!selfNeedsLayout()) {
                        ASSERT(r->m_originatingLine->renderer() == this);
                        r->m_originatingLine->markDirty();
                    }
#if !ASSERT_DISABLED
                    r->m_originatingLine = 0;
#endif
                }
                markLinesDirtyInBlockRange(0, logicalBottom);
            }
            m_floatingObjects->remove(r);
            ASSERT(!r->m_originatingLine);
            delete r;
        }
    }
}

void RenderBlock::removeFloatingObjectsBelow(FloatingObject* lastFloat, int logicalOffset)
{
    if (!m_floatingObjects)
        return;
    
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObject* curr = floatingObjectSet.last();
    while (curr != lastFloat && (!curr->isPlaced() || logicalTopForFloat(curr) >= logicalOffset)) {
        m_floatingObjects->remove(curr);
        ASSERT(!curr->m_originatingLine);
        delete curr;
        if (floatingObjectSet.isEmpty())
            break;
        curr = floatingObjectSet.last();
    }
}

LayoutPoint RenderBlock::computeLogicalLocationForFloat(const FloatingObject* floatingObject, LayoutUnit logicalTopOffset) const
{
    RenderBox* childBox = floatingObject->renderer();
    LayoutUnit logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset); // Constant part of right offset.
    LayoutUnit logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
    LayoutUnit floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset); // The width we look for.

    LayoutUnit floatLogicalLeft;

    if (childBox->style()->floating() == LeftFloat) {
        LayoutUnit heightRemainingLeft = 1;
        LayoutUnit heightRemainingRight = 1;
        floatLogicalLeft = logicalLeftOffsetForLine(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
        while (logicalRightOffsetForLine(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight) - floatLogicalLeft < floatLogicalWidth) {
            logicalTopOffset += min(heightRemainingLeft, heightRemainingRight);
            floatLogicalLeft = logicalLeftOffsetForLine(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
            if (inRenderFlowThread()) {
                // Have to re-evaluate all of our offsets, since they may have changed.
                logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset); // Constant part of right offset.
                logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
                floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
            }
        }
        floatLogicalLeft = max<LayoutUnit>(logicalLeftOffset - borderAndPaddingLogicalLeft(), floatLogicalLeft);
    } else {
        LayoutUnit heightRemainingLeft = 1;
        LayoutUnit heightRemainingRight = 1;
        floatLogicalLeft = logicalRightOffsetForLine(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
        while (floatLogicalLeft - logicalLeftOffsetForLine(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft) < floatLogicalWidth) {
            logicalTopOffset += min(heightRemainingLeft, heightRemainingRight);
            floatLogicalLeft = logicalRightOffsetForLine(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
            if (inRenderFlowThread()) {
                // Have to re-evaluate all of our offsets, since they may have changed.
                logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset); // Constant part of right offset.
                logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
                floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
            }
        }
        floatLogicalLeft -= logicalWidthForFloat(floatingObject); // Use the original width of the float here, since the local variable
                                                                  // |floatLogicalWidth| was capped to the available line width.
                                                                  // See fast/block/float/clamped-right-float.html.
    }
    
    return LayoutPoint(floatLogicalLeft, logicalTopOffset);
}

bool RenderBlock::positionNewFloats()
{
    if (!m_floatingObjects)
        return false;

    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    if (floatingObjectSet.isEmpty())
        return false;

    // If all floats have already been positioned, then we have no work to do.
    if (floatingObjectSet.last()->isPlaced())
        return false;

    // Move backwards through our floating object list until we find a float that has
    // already been positioned.  Then we'll be able to move forward, positioning all of
    // the new floats that need it.
    FloatingObjectSetIterator it = floatingObjectSet.end();
    --it; // Go to last item.
    FloatingObjectSetIterator begin = floatingObjectSet.begin();
    FloatingObject* lastPlacedFloatingObject = 0;
    while (it != begin) {
        --it;
        if ((*it)->isPlaced()) {
            lastPlacedFloatingObject = *it;
            ++it;
            break;
        }
    }

    LayoutUnit logicalTop = logicalHeight();
    
    // The float cannot start above the top position of the last positioned float.
    if (lastPlacedFloatingObject)
        logicalTop = max(logicalTopForFloat(lastPlacedFloatingObject), logicalTop);

    FloatingObjectSetIterator end = floatingObjectSet.end();
    // Now walk through the set of unpositioned floats and place them.
    for (; it != end; ++it) {
        FloatingObject* floatingObject = *it;
        // The containing block is responsible for positioning floats, so if we have floats in our
        // list that come from somewhere else, do not attempt to position them. Also don't attempt to handle
        // positioned floats, since the positioning layout code handles those.
        if (floatingObject->renderer()->containingBlock() != this || floatingObject->renderer()->isPositioned())
            continue;

        RenderBox* childBox = floatingObject->renderer();
        LayoutUnit childLogicalLeftMargin = style()->isLeftToRightDirection() ? marginStartForChild(childBox) : marginEndForChild(childBox);

        LayoutRect oldRect(childBox->x(), childBox->y() , childBox->width(), childBox->height());

        if (childBox->style()->clear() & CLEFT)
            logicalTop = max(lowestFloatLogicalBottom(FloatingObject::FloatLeft), logicalTop);
        if (childBox->style()->clear() & CRIGHT)
            logicalTop = max(lowestFloatLogicalBottom(FloatingObject::FloatRight), logicalTop);

        LayoutPoint floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, logicalTop);

        setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());
        setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
        setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

        if (view()->layoutState()->isPaginated()) {
            RenderBlock* childBlock = childBox->isRenderBlock() ? toRenderBlock(childBox) : 0;

            if (!childBox->needsLayout())
                childBox->markForPaginationRelayoutIfNeeded();
            childBox->layoutIfNeeded();

            // If we are unsplittable and don't fit, then we need to move down.
            // We include our margins as part of the unsplittable area.
            LayoutUnit newLogicalTop = adjustForUnsplittableChild(childBox, floatLogicalLocation.y(), true);
            
            // See if we have a pagination strut that is making us move down further.
            // Note that an unsplittable child can't also have a pagination strut, so this is
            // exclusive with the case above.
            if (childBlock && childBlock->paginationStrut()) {
                newLogicalTop += childBlock->paginationStrut();
                childBlock->setPaginationStrut(0);
            }
            
            if (newLogicalTop != floatLogicalLocation.y()) {
                floatingObject->m_paginationStrut = newLogicalTop - floatLogicalLocation.y();

                floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, newLogicalTop);
                setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());
                setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
                setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));
        
                if (childBlock)
                    childBlock->setChildNeedsLayout(true, false);
                childBox->layoutIfNeeded();
            }
        }

        setLogicalTopForFloat(floatingObject, floatLogicalLocation.y());
        setLogicalHeightForFloat(floatingObject, logicalHeightForChild(childBox) + marginBeforeForChild(childBox) + marginAfterForChild(childBox));

        m_floatingObjects->addPlacedObject(floatingObject);

        // If the child moved, we have to repaint it.
        if (childBox->checkForRepaintDuringLayout())
            childBox->repaintDuringLayoutIfMoved(oldRect);
    }
    return true;
}

void RenderBlock::newLine(EClear clear)
{
    positionNewFloats();
    // set y position
    int newY = 0;
    switch (clear)
    {
        case CLEFT:
            newY = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
            break;
        case CRIGHT:
            newY = lowestFloatLogicalBottom(FloatingObject::FloatRight);
            break;
        case CBOTH:
            newY = lowestFloatLogicalBottom();
        default:
            break;
    }
    if (height() < newY)
        setLogicalHeight(newY);
}

void RenderBlock::addPercentHeightDescendant(RenderBox* descendant)
{
    if (!gPercentHeightDescendantsMap) {
        gPercentHeightDescendantsMap = new PercentHeightDescendantsMap;
        gPercentHeightContainerMap = new PercentHeightContainerMap;
    }

    HashSet<RenderBox*>* descendantSet = gPercentHeightDescendantsMap->get(this);
    if (!descendantSet) {
        descendantSet = new HashSet<RenderBox*>;
        gPercentHeightDescendantsMap->set(this, descendantSet);
    }
    bool added = descendantSet->add(descendant).second;
    if (!added) {
        ASSERT(gPercentHeightContainerMap->get(descendant));
        ASSERT(gPercentHeightContainerMap->get(descendant)->contains(this));
        return;
    }

    HashSet<RenderBlock*>* containerSet = gPercentHeightContainerMap->get(descendant);
    if (!containerSet) {
        containerSet = new HashSet<RenderBlock*>;
        gPercentHeightContainerMap->set(descendant, containerSet);
    }
    ASSERT(!containerSet->contains(this));
    containerSet->add(this);
}

void RenderBlock::removePercentHeightDescendant(RenderBox* descendant)
{
    if (!gPercentHeightContainerMap)
        return;

    HashSet<RenderBlock*>* containerSet = gPercentHeightContainerMap->take(descendant);
    if (!containerSet)
        return;

    HashSet<RenderBlock*>::iterator end = containerSet->end();
    for (HashSet<RenderBlock*>::iterator it = containerSet->begin(); it != end; ++it) {
        RenderBlock* container = *it;
        HashSet<RenderBox*>* descendantSet = gPercentHeightDescendantsMap->get(container);
        ASSERT(descendantSet);
        if (!descendantSet)
            continue;
        ASSERT(descendantSet->contains(descendant));
        descendantSet->remove(descendant);
        if (descendantSet->isEmpty()) {
            gPercentHeightDescendantsMap->remove(container);
            delete descendantSet;
        }
    }

    delete containerSet;
}

HashSet<RenderBox*>* RenderBlock::percentHeightDescendants() const
{
    return gPercentHeightDescendantsMap ? gPercentHeightDescendantsMap->get(this) : 0;
}

#if !ASSERT_DISABLED
bool RenderBlock::hasPercentHeightDescendant(RenderBox* descendant)
{
    ASSERT(descendant);
    if (!gPercentHeightContainerMap)
        return false;
    HashSet<RenderBlock*>* containerSet = gPercentHeightContainerMap->take(descendant);
    return containerSet && containerSet->size();
}
#endif

template <RenderBlock::FloatingObject::Type FloatTypeValue>
inline void RenderBlock::FloatIntervalSearchAdapter<FloatTypeValue>::collectIfNeeded(const IntervalType& interval) const
{
    const FloatingObject* r = interval.data();
    if (r->type() == FloatTypeValue && interval.low() <= m_value && m_value < interval.high()) {
        // All the objects returned from the tree should be already placed.
        ASSERT(r->isPlaced() && m_renderer->logicalTopForFloat(r) <= m_value && m_renderer->logicalBottomForFloat(r) > m_value);

        if (FloatTypeValue == FloatingObject::FloatLeft 
            && m_renderer->logicalRightForFloat(r) > m_offset) {
            m_offset = m_renderer->logicalRightForFloat(r);
            if (m_heightRemaining)
                *m_heightRemaining = m_renderer->logicalBottomForFloat(r) - m_value;
        }

        if (FloatTypeValue == FloatingObject::FloatRight
            && m_renderer->logicalLeftForFloat(r) < m_offset) {
            m_offset = m_renderer->logicalLeftForFloat(r);
            if (m_heightRemaining)
                *m_heightRemaining = m_renderer->logicalBottomForFloat(r) - m_value;
        }
    }
}

LayoutUnit RenderBlock::textIndentOffset() const
{
    LayoutUnit cw = 0;
    if (style()->textIndent().isPercent())
        cw = containingBlock()->availableLogicalWidth();
    return style()->textIndent().calcMinValue(cw);
}

LayoutUnit RenderBlock::logicalLeftOffsetForContent(RenderRegion* region, LayoutUnit offsetFromLogicalTopOfFirstPage) const
{
    LayoutUnit logicalLeftOffset = style()->isHorizontalWritingMode() ? borderLeft() + paddingLeft() : borderTop() + paddingTop();
    if (!inRenderFlowThread())
        return logicalLeftOffset;
    LayoutRect boxRect = borderBoxRectInRegion(region, offsetFromLogicalTopOfFirstPage);
    return logicalLeftOffset + (isHorizontalWritingMode() ? boxRect.x() : boxRect.y());
}

LayoutUnit RenderBlock::logicalRightOffsetForContent(RenderRegion* region, LayoutUnit offsetFromLogicalTopOfFirstPage) const
{
    LayoutUnit logicalRightOffset = style()->isHorizontalWritingMode() ? borderLeft() + paddingLeft() : borderTop() + paddingTop();
    logicalRightOffset += availableLogicalWidth();
    if (!inRenderFlowThread())
        return logicalRightOffset;
    LayoutRect boxRect = borderBoxRectInRegion(region, offsetFromLogicalTopOfFirstPage);
    return logicalRightOffset - (logicalWidth() - (isHorizontalWritingMode() ? boxRect.maxX() : boxRect.maxY()));
}

LayoutUnit RenderBlock::logicalLeftOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
{
    LayoutUnit left = fixedOffset;
    if (m_floatingObjects && m_floatingObjects->hasLeftObjects()) {
        if (heightRemaining)
            *heightRemaining = 1;

        FloatIntervalSearchAdapter<FloatingObject::FloatLeft> adapter(this, logicalTop, left, heightRemaining);
        m_floatingObjects->placedFloatsTree().allOverlapsWithAdapter(adapter);
    }

    if (applyTextIndent && style()->isLeftToRightDirection())
        left += textIndentOffset();

    return left;
}

LayoutUnit RenderBlock::logicalRightOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
{
    LayoutUnit right = fixedOffset;
    if (m_floatingObjects && m_floatingObjects->hasRightObjects()) {
        if (heightRemaining)
            *heightRemaining = 1;

        LayoutUnit rightFloatOffset = fixedOffset;
        FloatIntervalSearchAdapter<FloatingObject::FloatRight> adapter(this, logicalTop, rightFloatOffset, heightRemaining);
        m_floatingObjects->placedFloatsTree().allOverlapsWithAdapter(adapter);
        right = min(right, rightFloatOffset);
    }
    
    if (applyTextIndent && !style()->isLeftToRightDirection())
        right -= textIndentOffset();
    
    return right;
}

LayoutUnit RenderBlock::nextFloatLogicalBottomBelow(LayoutUnit logicalHeight) const
{
    if (!m_floatingObjects)
        return logicalHeight;

    LayoutUnit bottom = numeric_limits<LayoutUnit>::max();
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* r = *it;
        LayoutUnit floatBottom = logicalBottomForFloat(r);
        if (floatBottom > logicalHeight)
            bottom = min(floatBottom, bottom);
    }

    return bottom == numeric_limits<LayoutUnit>::max() ? logicalHeight : bottom;
}

LayoutUnit RenderBlock::lowestFloatLogicalBottom(FloatingObject::Type floatType) const
{
    if (!m_floatingObjects)
        return 0;
    LayoutUnit lowestFloatBottom = 0;
    const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
    FloatingObjectSetIterator end = floatingObjectSet.end();
    for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
        FloatingObject* r = *it;
        if (r->isPlaced() && r->type() & floatType)
            lowestFloatBottom = max(lowestFloatBottom, logicalBottomForFloat(r));
    }
    return lowestFloatBottom;
}

void RenderBlock::markLinesDirtyInBlockRange(LayoutUnit logicalTop, LayoutUnit logicalBottom, RootInlineBox* highest)
{
    if (logicalTop >= logicalBottom)
        return;

    RootInlineBox* lowestDirtyLine = lastRootBox();
    RootInlineBox* afterLowest = lowestDirtyLine;
    while (lowestDirtyLine && lowestDirtyLine->lineBottomWithLeading() >= logicalBottom && logicalBottom < numeric_limits<LayoutUnit>::max()) {
        afterLowest = lowestDirtyLine;
        lowestDirtyLine = lowestDirtyLine->prevRootBox();
    }

    while (afterLowest && afterLowest != highest && (afterLowest->lineBottomWithLeading() >= logicalTop || afterLowest->lineBottomWithLeading() < 0)) {
        afterLowest->markDirty();
        afterLowest = afterLowest->prevRootBox();
    }
}

void RenderBlock::addPositionedFloats()