Reviewed by Ken.

    Reviewed by Ken.

        - fixed <rdar://problem/3803280> crash in selectAll on page with no contents

        * khtml/khtml_part.cpp: (KHTMLPart::selectAll): Handle case of 0 for documentElement().
        * khtml/xml/dom_position.cpp:
        (DOM::Position::previousWordPosition): Ditto.
        (DOM::Position::nextWordPosition): Ditto.

        - cleaned up caret code
        - changed DOM::Selection to use CaretPosition more

        * khtml/rendering/render_box.cpp: (RenderBox::caretRect): Change to use empty rectangles
        instead of an X value of -1 to mean no rectangle.
        * khtml/rendering/render_image.cpp: (RenderImage::selectionRect): Take advantage of the
        fixed QRect constructor.
        * khtml/rendering/render_object.cpp: (RenderObject::caretRect): Change to use empty
        rectangle instead of an X value of -1 to mean no rectangle.
        * khtml/rendering/render_text.cpp: (RenderText::caretRect): Cleaned up, and changed to use
        an empty rectangle instead of an X value of -1 to mean no rectangle.

        * khtml/xml/dom_caretposition.h: Made conversion from Position to CaretPosition something you
        can do implicitly, since it's an unambiguous conversion. Conversion in the other direction
        needs to be done explicitly. Moved EIncludeLineBreak here, and added startParagraphBoundary
        and endParagraphBoundary functions.
        * khtml/xml/dom_caretposition.cpp:
        (DOM::startParagraphBoundary): Added. Replaces, and made from, member function of DOM::Position.
        (DOM::endParagraphBoundary): Ditto.

        * khtml/xml/dom_position.h: Removed EIncludeLineBreak and startParagraphBoundary and
        endParagraphBoundary.
        * khtml/xml/dom_position.cpp: Removed startParagraphBoundary and endParagraphBoundary.

        * khtml/xml/dom_selection.h: Use CaretPosition instead of Position in a few places.
        Use a QRect for the caret rect. Change nodeIsBeforeNode to be a static member function.
        * khtml/xml/dom_selection.cpp:
        (DOM::Selection::Selection): Change caret to store QRect instead of 3 separate fields.
        (DOM::Selection::init): Ditto.
        (DOM::Selection::operator=): Ditto.
        (DOM::Selection::modifyExtendingRightForward): Change to use CaretPosition instead of Position.
        Check for 0.
        (DOM::Selection::modifyMovingRightForward): Ditto. Check for 0.
        (DOM::Selection::modifyExtendingLeftBackward): Ditto.
        (DOM::Selection::modifyMovingLeftBackward): Ditto.
        (DOM::Selection::modify): Ditto.
        (DOM::Selection::layoutCaret): Change to use a QRect for the caret rect, and use an empty
        one to mean no rectangle.
        (DOM::Selection::getRepaintRect): Ditto.
        (DOM::Selection::paintCaret): Ditto.
        (DOM::Selection::validate): Change to use CaretPosition instead of Position. Also fixed
        PARAGRAPH_BOUNDARY, which was broken and doing the same thing as PARAGRAPH before, but
        it's not really used so that didn't matter. Check for 0.
        (DOM::Selection::nodeIsBeforeNode): Tightened up a bit and added some FIXMEs. This function
        has a number of problems and should probably be discarded in favor of the DOMStringImpl
        method that does the same thing.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@7585 268f45cc-cd09-0410-ab3c-d52691b4dbfc