[CSS Regions] Selection highlight doesn't match DOM selection

[CSS Regions] Selection highlight doesn't match DOM selection
https://bugs.webkit.org/show_bug.cgi?id=131511

Reviewed by David Hyatt.

Source/WebCore:
This patch implements a subtrees approach to fix selection interaction in CSS Regions.

The idea is to divide the Render tree in subtrees. One subtree will be the RenderView (which is always present),
then for each RenderNamedFlowThread (which are children of RenderView) we will have an extra subtree.

For each subtree it determines the start and end positions according to the DOM tree. So, every subtree will
always have a start and end position, and the selection algorithm will be able to reach the end from the start
without problems (this allows us to remove the changes introduced in r155058).

Then selection related methods in RenderView are adapted to ensure that they are called for each subtree. Making
the selection highlight to match DOM selection as expected.

Test: fast/regions/selection/selecting-text-including-region.html

* CMakeLists.txt: Add new class SelectionSubtreeRoot to build file.
* WebCore.vcxproj/WebCore.vcxproj: Ditto.
* WebCore.vcxproj/WebCore.vcxproj.filters: Ditto.
* WebCore.xcodeproj/project.pbxproj: Ditto.
* rendering/RenderNamedFlowThread.h: Inherit from SelectionSubtreeRoot.
* rendering/RenderObject.cpp:
(WebCore::RenderObject::selectionRoot): New method to return the RenderNamedFlowThread if any or the RenderView
otherwise.
(WebCore::RenderObject::selectionStartEnd): If it's inside a RenderNamedFlowThread use specific method instead
of the RenderView's one.
* rendering/RenderObject.h: Add new method signature.
* rendering/RenderView.cpp:
(WebCore::RenderView::selectionBounds): Adapt method to subtrees approach.
(WebCore::RenderView::subtreeSelectionBounds): Modify previous method in order to use SelectionSubtreeRoot
objects.
(WebCore::RenderView::repaintSelection): Adapt method to subtrees approach.
(WebCore::RenderView::repaintSubtreeSelection): Modify previous method in order to use SelectionSubtreeRoot
objects.
(getNextOrPrevRenderObjectBasedOnDirection): Deleted method from r155058 as it is not needed anymore. Each
subtree will have start and end positions, so the selection algorithm will always find the end.
(WebCore::RenderView::setSelection): Adapt method to subtrees approach.
(WebCore::RenderView::splitSelectionBetweenSubtrees): Determine start and end positions for each subtree and
call setSubtreeSelection().
(WebCore::RenderView::setSubtreeSelection): Modify previous method in order to use SelectionSubtreeRoot objects.
* rendering/RenderView.h: Inherit from SelectionSubtreeRoot. Add signature for new helper methods receiving
SelectionSubtreeRoot objects.
* rendering/SelectionSubtreeRoot.cpp: Added.
(WebCore::SelectionSubtreeRoot::SelectionSubtreeRoot):
(WebCore::SelectionSubtreeRoot::selectionStartEndPositions):
* rendering/SelectionSubtreeRoot.h: Added. New class to identify root elements for the subtrees. With some basic
attributes and methods to store the start and end positions and offsets.
(WebCore::SelectionSubtreeRoot::selectionStart):
(WebCore::SelectionSubtreeRoot::selectionStartPos):
(WebCore::SelectionSubtreeRoot::selectionEnd):
(WebCore::SelectionSubtreeRoot::selectionEndPos):
(WebCore::SelectionSubtreeRoot::setSelectionStart):
(WebCore::SelectionSubtreeRoot::setSelectionStartPos):
(WebCore::SelectionSubtreeRoot::setSelectionEnd):
(WebCore::SelectionSubtreeRoot::setSelectionEndPos):

LayoutTests:
Add new test to check highlight of render objects moved under RenderNamedFlowThread in the render tree.

Updated some tests to avoid issues with selection gap filling in the new implementation.

* fast/regions/selection/selecting-text-including-region-expected.html: Added.
* fast/regions/selection/selecting-text-including-region.html: Added.
* fast/regions/selection/selecting-text-through-different-region-flows-2-expected.html: Updated.
* fast/regions/selection/selecting-text-through-different-region-flows-2.html: Updated.
* fast/regions/selection/selection-direction-expected.html: Updated.
* fast/regions/selection/selection-direction.html: Updated.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167652 268f45cc-cd09-0410-ab3c-d52691b4dbfc