Detect change on the intersection of video and viewport.

third_party/WebKit/public/platform/WebMediaPlayer.h

Index: third_party/WebKit/public/platform/WebMediaPlayer.h
diff --git a/third_party/WebKit/public/platform/WebMediaPlayer.h b/third_party/WebKit/public/platform/WebMediaPlayer.h
index 792328531796a3b0b2a1c7f682cfdaf51f79012e..f82ba332d088577d3da9e1947584173322edb931 100644
--- a/third_party/WebKit/public/platform/WebMediaPlayer.h
+++ b/third_party/WebKit/public/platform/WebMediaPlayer.h
@@ -229,6 +229,10 @@ class WebMediaPlayer {
   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.