[Chromecast] Fix media session blocking tests.

content/browser/media/session/media_session_impl.h

Index: content/browser/media/session/media_session_impl.h
diff --git a/content/browser/media/session/media_session_impl.h b/content/browser/media/session/media_session_impl.h
index a34699ae2a7bb9f2a8893bb732f3688528da9478..6ed0ce44b981307427d2c27605c3c215946c8cab 100644
--- a/content/browser/media/session/media_session_impl.h
+++ b/content/browser/media/session/media_session_impl.h
@@ -85,9 +85,6 @@ class MediaSessionImpl : public MediaSession,
   }
 #endif  // defined(OS_ANDROID)
 
-  void AddObserver(MediaSessionObserver* observer);
-  void RemoveObserver(MediaSessionObserver* observer);
-
   void NotifyMediaSessionMetadataChange(
       const base::Optional<MediaMetadata>& metadata);
   void NotifyMediaSessionActionsChange(
@@ -138,6 +135,9 @@ class MediaSessionImpl : public MediaSession,
   // recovered.
   CONTENT_EXPORT void StopDucking() override;
 
+  void AddObserver(MediaSessionObserver* observer) override;
+  void RemoveObserver(MediaSessionObserver* observer) override;
+
   // Returns if the session can be controlled by Resume() and Suspend calls
   // above.
   CONTENT_EXPORT bool IsControllable() const;