https://bugs.webkit.org/show_bug.cgi?id=113479

Reviewed by David Hyatt.

Introduced LogicalSelectionOffsetCaches to cache the containing blocks and their logical left and right
selection offsets in computing selection gaps. An instance of this class stores the containing block for
each position type and caches their logical selection offsets when none of their block ancestors up until
its nearest selection root do no have any floating objects or regions and exclusions.

When blockSelectionGaps recurses to another level, it creates a new cache instance by "inheriting"
(like RenderStyle) from the old cache, overriding those containing blocks that are replaced by "this".

This eliminates the need to traverse containing block ancestors in RenderBlock::logicalLeftSelectionOffset
and RenderBlock::logicalRightSelectionOffset, and improves WebKit's performance by roughly 20%.

Performance Tests: Interactive/SelectAll.html

* GNUmakefile.list.am:
* Target.pri:
* WebCore.xcodeproj/project.pbxproj:

* rendering/LogicalSelectionOffsetCaches.h: Added.
(WebCore::isContainingBlockCandidateForAbsolutelyPositionedObject): Moved from RenderObject.h.
(WebCore::isNonRenderBlockInline): Ditto.
(WebCore::containingBlockForFixedPosition): Extracted from RenderObject::containingBlock.
(WebCore::containingBlockForAbsolutePosition): Ditto.
(WebCore::containingBlockForObjectInFlow): Ditto.

(WebCore::LogicalSelectionOffsetCaches): Added.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::ContainingBlockInfo): Added.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::setBlock): Added. m_hasFloatsOrRegions is
or'ed with itself when ContainingBlockInfo is copy constructed since m_hasFloatsOrRegions needs be true
for a block when any of its containing block ancestors have floats or regions.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::block): Added.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::cache): Added.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::logicalLeftSelectionOffset): Added. Caches
the logical selection offset if it hasn't.
(WebCore::LogicalSelectionOffsetCaches::ContainingBlockInfo::logicalRightSelectionOffset): Ditto.

(WebCore::LogicalSelectionOffsetCaches::LogicalSelectionOffsetCaches): The first constructor is used
for a selection root. The second one is used for inheriting from another cache. In the latter case,
copy all containing block information except ones that need to be overridden by this block.
(WebCore::LogicalSelectionOffsetCaches::containingBlockInfo): Returns a ContainingBlockInfo based on
object's position value.

* rendering/RenderBlock.cpp:
(WebCore::RenderBlock::selectionGapRectsForRepaint):
(WebCore::RenderBlock::paintSelection):
(WebCore::RenderBlock::selectionGaps):
(WebCore::RenderBlock::inlineSelectionGaps):
(WebCore::RenderBlock::blockSelectionGaps): Exit before instantiating a new LogicalSelectionOffsetCaches
if there is no child to recurse.
(WebCore::RenderBlock::blockSelectionGap):
(WebCore::RenderBlock::logicalLeftSelectionGap):
(WebCore::RenderBlock::logicalRightSelectionGap):
(WebCore::RenderBlock::logicalLeftSelectionOffset): Use LogicalSelectionOffsetCaches to get its containing
block and its logical selection offset.
(WebCore::RenderBlock::logicalRightSelectionOffset): Ditto.

* rendering/RenderBlock.h:
(WebCore::RenderBlock):

* rendering/RenderObject.cpp:
(WebCore::RenderObject::containingBlock): Extracted code into LogicalSelectionOffsetCaches.h.

* rendering/RootInlineBox.cpp:
(WebCore::RootInlineBox::lineSelectionGap):

* rendering/RootInlineBox.h:
(WebCore::RootInlineBox):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149007 268f45cc-cd09-0410-ab3c-d52691b4dbfc