Detect change on the intersection of video and viewport.

third_party/WebKit/public/platform/WebMediaPlayer.h

 /*
  * Copyright (C) 2009 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 211 matching lines @@
 
   // Whether the WebMediaPlayer supports overlay fullscreen video mode. When
   // this is true, the video layer will be removed from the layer tree when
   // entering fullscreen, and the WebMediaPlayer is responsible for displaying
   // the video in enteredFullscreen().
   virtual bool supportsOverlayFullscreenVideo() { return false; }
   // Inform WebMediaPlayer when the element has entered/exited fullscreen.
   virtual void enteredFullscreen() {}
   virtual void exitedFullscreen() {}
 
+  // Inform WebMediaPlayer when the element starts/stops being the dominant
+  // visible content.
+  virtual void becameDominantVisibleContent(bool isDominant) {}
+
   virtual void enabledAudioTracksChanged(
       const WebVector<TrackId>& enabledTrackIds) {}
   // |selectedTrackId| is null if no track is selected.
   virtual void selectedVideoTrackChanged(TrackId* selectedTrackId) {}
 };
 
 }  // namespace blink
 
 #endif