Plumb CompositingReason from Blink to compositor.

Source/core/rendering/RenderLayerBacking.h

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 215 matching lines @@
     // Returns true if this layer has content that needs to be rendered by painting into the backing store.
     bool containsPaintedContent() const;
     // Returns true if the RenderLayer just contains an image that we can composite directly.
     bool isDirectlyCompositedImage() const;
     void updateImageContents();
 
     Color rendererBackgroundColor() const;
     void updateBackgroundColor(bool isSimpleContainer);
     void updateContentsRect(bool isSimpleContainer);
 
+    void updateCompositingReasons();
+
     bool hasVisibleNonCompositingDescendantLayers() const;
 
     bool shouldClipCompositedBounds() const;
 
     void paintIntoLayer(const GraphicsLayer*, GraphicsContext*, const IntRect& paintDirtyRect, PaintBehavior, GraphicsLayerPaintingPhase);
 
     static CSSPropertyID graphicsLayerToCSSProperty(AnimatedPropertyID);
     static AnimatedPropertyID cssToGraphicsLayerProperty(CSSPropertyID);
 
     RenderLayer* m_owningLayer;
@@ skipping 21 matching lines @@
     bool m_boundsConstrainedByClipping;
     bool m_isMainFrameRenderViewLayer;
     bool m_requiresOwnBackingStore;
     bool m_canCompositeFilters;
     bool m_backgroundLayerPaintsFixedRootBackground;
 };
 
 } // namespace WebCore
 
 #endif // RenderLayerBacking_h