[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..2169c178e32a57f2cdb043f9496c5075cfc76193 100644
--- a/content/browser/media/session/media_session_impl.h
+++ b/content/browser/media/session/media_session_impl.h
@@ -8,12 +8,12 @@
 #include <stddef.h>
 
 #include <map>
+#include <memory>
 #include <set>
 
 #include "base/callback_list.h"
 #include "base/id_map.h"
 #include "base/macros.h"
-#include "base/observer_list.h"
 #include "base/optional.h"
 #include "content/browser/media/session/audio_focus_manager.h"
 #include "content/browser/media/session/media_session_uma_helper.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(
@@ -296,8 +293,6 @@ class MediaSessionImpl : public MediaSession,
 
   base::CallbackList<void(State)> media_session_state_listeners_;
 
-  base::ObserverList<MediaSessionObserver> observers_;
-
 #if defined(OS_ANDROID)
   std::unique_ptr<MediaSessionAndroid> session_android_;
 #endif  // defined(OS_ANDROID)