Use observer pattern instead of sniffing SwapCompositorFrame IPC

content/browser/renderer_host/render_widget_host_delegate.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_DELEGATE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_DELEGATE_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 231 matching lines @@
 
   // Notifies the delegate that a focused editable element has been touched
   // inside this RenderWidgetHost. If |editable| is true then the focused
   // element accepts text input.
   virtual void FocusedNodeTouched(bool editable) {}
 
   // Return this object cast to a WebContents, if it is one. If the object is
   // not a WebContents, returns nullptr.
   virtual WebContents* GetAsWebContents();
 
+  // Notifies that a CompositorFrame was received from the renderer.
+  virtual void DidReceiveCompositorFrame() {}
+
  protected:
   virtual ~RenderWidgetHostDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_DELEGATE_H_