[Video] MediaSession API event handlers can resume background video.

third_party/WebKit/public/platform/WebMediaPlayerClient.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 76 matching lines @@
   virtual void addTextTrack(WebInbandTextTrack*) = 0;
   virtual void removeTextTrack(WebInbandTextTrack*) = 0;
   virtual void mediaSourceOpened(WebMediaSource*) = 0;
   virtual void requestSeek(double) = 0;
   virtual void remoteRouteAvailabilityChanged(
       WebRemotePlaybackAvailability) = 0;
   virtual void connectedToRemoteDevice() = 0;
   virtual void disconnectedFromRemoteDevice() = 0;
   virtual void cancelledRemotePlaybackRequest() = 0;
   virtual void remotePlaybackStarted() = 0;
+  virtual void wasBackgrounded() = 0;
 
   // After the monitoring is activated, the client will inform WebMediaPlayer
   // when the element becomes/stops being the dominant visible content by
   // calling WebMediaPlayer::becameDominantVisibleContent(bool).
   virtual void activateViewportIntersectionMonitoring(bool) {}
 
   // Returns whether the media element is in an autoplay muted state.
   virtual bool isAutoplayingMuted() = 0;
 
   // Warning: This method will destruct the caller.
   virtual void requestReload(const WebURL& newUrl) = 0;
 
   // Returns if there's a selected video track.
   virtual bool hasSelectedVideoTrack() = 0;
 
   // Returns the selected video track id (or an empty id if there's none).
   virtual WebMediaPlayer::TrackId getSelectedVideoTrackId() = 0;
 
+  // Returns if the background video playback was unlocked by user gesture.
+  virtual bool isBackgroundVideoPlaybackUnlocked() = 0;
+
  protected:
   ~WebMediaPlayerClient() {}
 };
 
 }  // namespace blink
 
 #endif