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 2850 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));

[ojan, 2014/01/03 02:04:26]

I'm still not sure this is correct. For example, the containingBlock can change
if this is a position:absolute and one of it's ancestors gets set to
position:relative dynamically. Then we will be in a situation where don't know
if there's a percentage height descendant that we need to update and
dirtyForLayoutFromPercentageHeightDescendants will do the wrong thing.

I'm not sure. Maybe I'm wrong.

[Xianzhu, 2014/01/03 20:46:24]

Actually percentHeightDescendants set doesn't include positioned descendants
whose heights are calculated in another path than
RenderBox::computePercentageLogicalHeight(). Non-positioned boxes won't change
containing block in this way. I'm investigating this further to make sure.
Perhaps I need to add some asserts.

 
     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 144 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())
                 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 1904 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore