android: Add draw completion for CompositorView

content/public/browser/android/compositor_client.h

 // Copyright 2013 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_PUBLIC_BROWSER_ANDROID_COMPOSITOR_CLIENT_H_
 #define CONTENT_PUBLIC_BROWSER_ANDROID_COMPOSITOR_CLIENT_H_
 
 #include "base/macros.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class CONTENT_EXPORT CompositorClient {
  public:
   // Gives the client a chance to update the layer tree host before compositing.
   virtual void UpdateLayerTreeHost() {}
 
-  // The compositor has completed swapping a frame.
+  // The compositor has completed swapping a frame. This is a subset of
+  // DidSwapBuffers and corresponds only to frames where Compositor submits a
+  // new frame.
   virtual void DidSwapFrame(int pending_frames) {}
 
+  // This is called on all swap buffers, regardless of cause.
+  virtual void DidSwapBuffers() {}
+
  protected:
   CompositorClient() {}
   virtual ~CompositorClient() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CompositorClient);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_ANDROID_COMPOSITOR_CLIENT_H_