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

third_party/WebKit/public/platform/WebMediaPlayerClient.h

Index: third_party/WebKit/public/platform/WebMediaPlayerClient.h
diff --git a/third_party/WebKit/public/platform/WebMediaPlayerClient.h b/third_party/WebKit/public/platform/WebMediaPlayerClient.h
index 192c94607fc8ff07e093885ee93a49e78f050eeb..37677d6852c3666c8d538058fbd1c746311e815d 100644
--- a/third_party/WebKit/public/platform/WebMediaPlayerClient.h
+++ b/third_party/WebKit/public/platform/WebMediaPlayerClient.h
@@ -94,6 +94,7 @@ class BLINK_PLATFORM_EXPORT WebMediaPlayerClient {
   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
@@ -112,6 +113,9 @@ class BLINK_PLATFORM_EXPORT WebMediaPlayerClient {
   // 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() {}
 };