Implement MediaSession on top of the WebMediaPlayerDelegate.

media/blink/webmediaplayer_impl.h

Index: media/blink/webmediaplayer_impl.h
diff --git a/media/blink/webmediaplayer_impl.h b/media/blink/webmediaplayer_impl.h
index ba03528cde0586e5ed147673922c16c0f41b3545..4ae7cf98b688038ebdf1e3d80cb1d3543d914461 100644
--- a/media/blink/webmediaplayer_impl.h
+++ b/media/blink/webmediaplayer_impl.h
@@ -194,6 +194,9 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   // WebMediaPlayerDelegate::Observer implementation.
   void OnHidden() override;
   void OnShown() override;
+  void OnPlay() override;
+  void OnPause() override;
+  void OnVolumeMultiplierUpdate(double multiplier) override;
 
 #if defined(OS_ANDROID)  // WMPI_CAST
   bool isRemote() const override;
@@ -434,6 +437,9 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   WebMediaPlayerCast cast_impl_;
 #endif
 
+  double volume_;
+  double volume_multiplier_;
+
   scoped_ptr<RendererFactory> renderer_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerImpl);