Add tests and settings plumbing for accelerated fixed root background

Source/core/platform/graphics/GraphicsLayerClient.h

 /*
  * Copyright (C) 2009 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 39 matching lines @@
     AnimatedPropertyWebkitTransform,
     AnimatedPropertyOpacity,
     AnimatedPropertyBackgroundColor,
     AnimatedPropertyWebkitFilter
 };
 
 enum {
     LayerTreeNormal = 0,
     LayerTreeIncludesDebugInfo = 1 << 0, // Dump extra debugging info like layer addresses.
     LayerTreeIncludesRepaintRects = 1 << 1,
-    LayerTreeIncludesPaintingPhases = 1 << 2
+    LayerTreeIncludesPaintingPhases = 1 << 2,
+    LayerTreeIncludesRootLayer = 1 << 3
 };
 typedef unsigned LayerTreeFlags;
 
 class GraphicsLayerClient {
 public:
     virtual ~GraphicsLayerClient() {}
 
     // Callback for when hardware-accelerated animation started.
     virtual void notifyAnimationStarted(const GraphicsLayer*, double time) = 0;
 
@@ skipping 12 matching lines @@
     // This is executed in GraphicsLayer construction and destruction
     // to verify that we don't create or destroy GraphicsLayers
     // while painting.
     virtual void verifyNotPainting() { }
 #endif
 };
 
 } // namespace WebCore
 
 #endif // GraphicsLayerClient_h