Fix Compositing of Opaque Scrolling Layers and Add Tests

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.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 199 matching lines @@
         return m_squashingLayerOffsetFromTransformedAncestor;
     }
 
     // If there is a squashed layer painting into this CLM that is an ancestor of the given LayoutObject, return it. Otherwise return nullptr.
     const GraphicsLayerPaintInfo* containingSquashedLayer(const LayoutObject*, unsigned maxSquashedLayerIndex);
 
     void updateScrollingBlockSelection();
 
     void adjustForCompositedScrolling(const GraphicsLayer*, IntSize& offset) const;
 
-    // Returns true for layers with scrollable overflow which have a background
-    // that can be painted into the composited scrolling contents layer (i.e.
-    // the background can scroll with the content). When the background is also
-    // opaque this allows us to composite the scroller even on low DPI as we can
-    // draw with subpixel anti-aliasing.
-    bool shouldPaintBackgroundOntoScrollingContentsLayer() const;
-
 private:
     IntRect recomputeInterestRect(const GraphicsLayer*) const;
     static bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize);
 
     static const GraphicsLayerPaintInfo* containingSquashedLayer(const LayoutObject*,  const Vector<GraphicsLayerPaintInfo>& layers, unsigned maxSquashedLayerIndex);
 
     // Paints the scrollbar part associated with the given graphics layer into the given context.
     void paintScrollableArea(const GraphicsLayer*, GraphicsContext&, const IntRect& interestRect) const;
     // Returns whether the given layer is part of the scrollable area, if any, associated with this mapping.
     bool isScrollableAreaLayer(const GraphicsLayer*) const;
@@ skipping 223 matching lines @@
 
     unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
     unsigned m_scrollingContentsAreEmpty : 1;
 
     friend class CompositedLayerMappingTest;
 };
 
 } // namespace blink
 
 #endif // CompositedLayerMapping_h