Reland "Avoid layout/full-repaint on view height change if possible"

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index 4a2d54b7400e91504c480135fbf3b3e1b727fabb..60ece9d82187a1107b570e2a2a3a2a2834a4164e 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -2708,8 +2708,8 @@ LayoutUnit RenderBox::computePercentageLogicalHeight(const Length& height) const
         skippedAutoHeightContainingBlock = true;
         containingBlockChild = cb;
         cb = cb->containingBlock();
-        cb->addPercentHeightDescendant(const_cast<RenderBox*>(this));
     }
+    cb->addPercentHeightDescendant(const_cast<RenderBox*>(this));

[esprehn, 2014/03/10 21:32:30]

Same, why is it okay to skip adding percentage height descendants inside the
loop now?

[Xianzhu, 2014/03/11 00:55:13]

In existing code, percentHeightDescendants is used to force layout of an object
whose height is percentage height related to an ancestor. The intermediate
containing blocks are skipped because they don't contribute to the calculation
of the object's height, so it's unnecessary to add the object into the
intermediate containing blocks percentHeightDescendants, except the last cb.

However, because the addPercentHeightDescendant call is in the loop, it is only
called if there is any containing block skipped. That is, it is called for each
percent height grand-child or lower descendant child, but not for direct child.
This was intentional when the change was made because layout of direct children
doesn't depend on the percentHeightDescendant map.  For my change, a block needs
to know all of its descendants (including direct children) whose layout may be
affected by the height of the block, so I moved an addPercentHeightDescendent()
call after the loop.

 
     RenderStyle* cbstyle = cb->style();
 
@@ -2861,10 +2861,10 @@ LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) co
         case Calculated:
         {
             RenderObject* cb = isOutOfFlowPositioned() ? container() : containingBlock();
-            while (cb->isAnonymous()) {
+            while (cb->isAnonymous())
                 cb = cb->containingBlock();
+            if (cb->isRenderBlock())

[esprehn, 2014/03/10 21:32:30]

This skips adding anonymous percentage height descendants, why is that correct?

[Xianzhu, 2014/03/11 00:55:13]

Actually this skips adding this object into percentHeightDescendants of
anonymous ancestors. By moving the call after the loop, this object is added
into the ancestor who really affects the height of this object.

                 toRenderBlock(cb)->addPercentHeightDescendant(const_cast<RenderBox*>(this));
-            }
 
             // FIXME: This calculation is not patched for block-flow yet.
             // https://bugs.webkit.org/show_bug.cgi?id=46500