Direct composite canvas background if possible.

Source/core/rendering/RenderVideo.h

 /*
  * Copyright (C) 2007, 2009, 2010 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 67 matching lines @@
 
     LayoutSize m_cachedImageSize;
 };
 
 inline RenderVideo* toRenderVideo(RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isVideo());
     return static_cast<RenderVideo*>(object);
 }
 
+inline const RenderVideo* toRenderVideo(const RenderObject* object)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isVideo());
+    return static_cast<const RenderVideo*>(object);
+}
+
 // This will catch anyone doing an unnecessary cast.
 void toRenderVideo(const RenderVideo*);
 
 } // namespace WebCore
 
 #endif // RenderVideo_h