Refactor the way PaintArtifactCompositor is attached and used.

third_party/WebKit/Source/web/WebFrameWidgetImpl.h

 /*
  * Copyright (C) 2014 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 120 matching lines @@
     Element* focusedElement() const;
 
     PaintLayerCompositor* compositor() const;
 
     // WebFrameWidgetBase overrides:
     bool forSubframe() const override { return true; }
     void scheduleAnimation() override;
     CompositorProxyClient* createCompositorProxyClient() override;
     WebWidgetClient* client() const override { return m_client; }
     void setRootGraphicsLayer(GraphicsLayer*) override;
+    void setRootLayer(WebLayer*) override;
     void attachCompositorAnimationTimeline(CompositorAnimationTimeline*) override;
     void detachCompositorAnimationTimeline(CompositorAnimationTimeline*) override;
 
     // Exposed for the purpose of overriding device metrics.
     void sendResizeEventAndRepaint();
 
     void updateMainFrameLayoutSize();
 
     void setIgnoreInputEvents(bool newValue);
 
@@ skipping 100 matching lines @@
     WebColor m_baseBackgroundColor;
 
     SelfKeepAlive<WebFrameWidgetImpl> m_selfKeepAlive;
 };
 
 DEFINE_TYPE_CASTS(WebFrameWidgetImpl, WebFrameWidgetBase, widget, widget->forSubframe(), widget.forSubframe());
 
 } // namespace blink
 
 #endif