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

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "core/frame/FrameView.h"
@@ skipping 123 matching lines @@
 bool CompositingReasonFinder::requiresCompositingForFilters(RenderObject* renderer) const
 {
     if (!(m_compositingTriggers & FilterTrigger))
         return false;
 
     return renderer->hasFilter();
 }
 
 bool CompositingReasonFinder::requiresCompositingForWillChangeCompositingHint(const RenderObject* renderer) const
 {
+    if (renderer->style()->subtreeWillChangeContents())
+        return false;
+
     return renderer->style()->hasWillChangeCompositingHint();
 }
 
 CompositingReasons CompositingReasonFinder::nonStyleDeterminedDirectReasons(const RenderLayer* layer, bool* needToRecomputeCompositingRequirements) const
 {
     CompositingReasons directReasons = CompositingReasonNone;
     RenderObject* renderer = layer->renderer();
 
     if (hasOverflowScrollTrigger()) {
         if (requiresCompositingForOutOfFlowClipping(layer))
@@ skipping 13 matching lines @@
         directReasons |= CompositingReasonPositionFixed;
 
     directReasons |= renderer->additionalCompositingReasons(m_compositingTriggers);
 
     ASSERT(!(directReasons & CompositingReasonComboAllStyleDeterminedReasons));
     return directReasons;
 }
 
 bool CompositingReasonFinder::requiresCompositingForAnimation(RenderObject* renderer) const
 {
+    if (renderer->style()->subtreeWillChangeContents())
+        return renderer->style()->isRunningAnimationOnCompositor();
+
     return renderer->style()->shouldCompositeForCurrentAnimations();
 }
 
 bool CompositingReasonFinder::requiresCompositingForOutOfFlowClipping(const RenderLayer* layer) const
 {
     return layer->isUnclippedDescendant();
 }
 
 bool CompositingReasonFinder::requiresCompositingForOverflowScrollingParent(const RenderLayer* layer) const
 {
@@ skipping 95 matching lines @@
                 *needToRecomputeCompositingRequirements = true;
             }
             return false;
         }
     }
 
     return true;
 }
 
 }