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

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 2690 matching lines @@
     bool skippedAutoHeightContainingBlock = false;
     RenderBlock* cb = containingBlock();
     const RenderBox* containingBlockChild = this;
     LayoutUnit rootMarginBorderPaddingHeight = 0;
     while (!cb->isRenderView() && skipContainingBlockForPercentHeightCalculation(cb)) {
         if (cb->isBody() || cb->isRoot())
             rootMarginBorderPaddingHeight += cb->marginBefore() + cb->marginAfter() + cb->borderAndPaddingLogicalHeight();
         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();
 
     // A positioned element that specified both top/bottom or that specifies height should be treated as though it has a height
     // explicitly specified that can be used for any percentage computations.
     bool isOutOfFlowPositionedWithSpecifiedHeight = cb->isOutOfFlowPositioned() && (!cbstyle->logicalHeight().isAuto() || (!cbstyle->logicalTop().isAuto() && !cbstyle->logicalBottom().isAuto()));
 
     bool includeBorderPadding = isTable();
 
     if (isHorizontalWritingMode() != cb->isHorizontalWritingMode())
@@ skipping 131 matching lines @@
 
 LayoutUnit RenderBox::computeReplacedLogicalHeightUsing(Length logicalHeight) const
 {
     switch (logicalHeight.type()) {
         case Fixed:
             return adjustContentBoxLogicalHeightForBoxSizing(logicalHeight.value());
         case Percent:
         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
             if (cb->isOutOfFlowPositioned() && cb->style()->height().isAuto() && !(cb->style()->top().isAuto() || cb->style()->bottom().isAuto())) {
                 ASSERT_WITH_SECURITY_IMPLICATION(cb->isRenderBlock());
                 RenderBlock* block = toRenderBlock(cb);
                 LogicalExtentComputedValues computedValues;
                 block->computeLogicalHeight(block->logicalHeight(), 0, computedValues);
                 LayoutUnit newContentHeight = computedValues.m_extent - block->borderAndPaddingLogicalHeight() - block->scrollbarLogicalHeight();
                 LayoutUnit newHeight = block->adjustContentBoxLogicalHeightForBoxSizing(newContentHeight);
@@ skipping 1808 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore