Split MediaSessionStateChanged() and MediaSessionMetadataChanged()

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index 73f87244d72687ef8fac406d65db68aa61ac0a88..75068a8677a24569873faf4f684b1e366bd1d93c 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -469,9 +469,11 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   virtual void MediaStoppedPlaying(const MediaPlayerId& id) {}
 
   // Invoked when media session has changed its state.
-  virtual void MediaSessionStateChanged(
-      bool is_controllable,
-      bool is_suspended,
+  virtual void MediaSessionStateChanged(bool is_controllable,
+                                        bool is_suspended) {}
+
+  // Invoked when media session metadata has changed.

[clamy, 2016/10/12 12:25:04]

Could you add a comment explaining that |metadata| means that a previous
metadata should be unset?

[Zhiqiang Zhang (Slow), 2016/10/12 12:41:16]

Done.

+  virtual void MediaSessionMetadataChanged(
       const base::Optional<MediaMetadata>& metadata) {}
 
   // Invoked when the renderer process changes the page scale factor.