Paint solid color background into both scrolling contents layer and graphics layer.

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 645 matching lines @@
   unsigned m_pendingUpdateScope : 2;
   unsigned m_isMainFrameLayoutViewLayer : 1;
 
   unsigned m_backgroundLayerPaintsFixedRootBackground : 1;
   unsigned m_scrollingContentsAreEmpty : 1;
 
   // Keep track of whether the background is painted onto the scrolling contents
   // layer for invalidations.
   unsigned m_backgroundPaintsOntoScrollingContentsLayer : 1;
 
+  // Solid color border boxes may be painted into both the scrolling contents
+  // layer and the graphics layer because the scrolling contents layer is
+  // clipped by the padding box.
+  unsigned m_backgroundPaintsOntoGraphicsLayer : 1;
+
   friend class CompositedLayerMappingTest;
 };
 
 }  // namespace blink
 
 #endif  // CompositedLayerMapping_h