Make 'will-change: contents' suppress compositing in subtree

Source/core/css/resolver/StyleBuilderCustom.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
@@ skipping 1063 matching lines @@
         t |= t2;
     }
     state.style()->setTextUnderlinePosition(static_cast<TextUnderlinePosition>(t));
 }
 
 void StyleBuilderFunctions::applyInitialCSSPropertyWillChange(StyleResolverState& state)
 {
     state.style()->setWillChangeContents(false);
     state.style()->setWillChangeScrollPosition(false);
     state.style()->setWillChangeProperties(Vector<CSSPropertyID>());
+    state.style()->setSubtreeWillChangeContents(state.parentStyle()->subtreeWillChangeContents());

[esprehn, 2014/05/23 01:05:58]

I don't think this is correct, we don't go through the initial setter normally.
This is only if you do will-change: initial;

[ajuma, 2014/05/23 14:38:31]

For the normal case, RenderStyle::inheritFrom already does:
  rareInheritedData = inheritParent->rareInheritedData;
so we don't need to add any additional logic there.

(But the logic added above is indeed needed for when you do "will-change:
initial".)

 }
 
 void StyleBuilderFunctions::applyInheritCSSPropertyWillChange(StyleResolverState& state)
 {
     state.style()->setWillChangeContents(state.parentStyle()->willChangeContents());
     state.style()->setWillChangeScrollPosition(state.parentStyle()->willChangeScrollPosition());
     state.style()->setWillChangeProperties(state.parentStyle()->willChangeProperties());
+    state.style()->setSubtreeWillChangeContents(state.parentStyle()->subtreeWillChangeContents());
 }
 
 void StyleBuilderFunctions::applyValueCSSPropertyWillChange(StyleResolverState& state, CSSValue* value)
 {
     ASSERT(value->isValueList());
     bool willChangeContents = false;
     bool willChangeScrollPosition = false;
     Vector<CSSPropertyID> willChangeProperties;
 
     for (CSSValueListIterator i(value); i.hasMore(); i.advance()) {
         CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(i.value());
         if (CSSPropertyID propertyID = primitiveValue->getPropertyID())
             willChangeProperties.append(propertyID);
         else if (primitiveValue->getValueID() == CSSValueContents)
             willChangeContents = true;
         else if (primitiveValue->getValueID() == CSSValueScrollPosition)
             willChangeScrollPosition = true;
         else
             ASSERT_NOT_REACHED();
     }
     state.style()->setWillChangeContents(willChangeContents);
     state.style()->setWillChangeScrollPosition(willChangeScrollPosition);
     state.style()->setWillChangeProperties(willChangeProperties);
+    state.style()->setSubtreeWillChangeContents(willChangeContents || state.parentStyle()->subtreeWillChangeContents());
 }
 
 void StyleBuilderFunctions::applyInitialCSSPropertyContent(StyleResolverState& state)
 {
     state.style()->clearContent();
 }
 
 void StyleBuilderFunctions::applyInheritCSSPropertyContent(StyleResolverState&)
 {
     // FIXME: In CSS3, it will be possible to inherit content. In CSS2 it is not. This
@@ skipping 250 matching lines @@
         default:
             break;
         }
     } else {
         svgStyle->setBaselineShift(BS_LENGTH);
         svgStyle->setBaselineShiftValue(SVGLength::fromCSSPrimitiveValue(primitiveValue));
     }
 }
 
 } // namespace WebCore