[Chromecast] Fix media session blocking tests.

content/public/browser/media_session_observer.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_
 
 #include <set>
 
 #include "base/macros.h"
 #include "base/optional.h"
 #include "content/common/content_export.h"
 #include "content/public/common/media_metadata.h"
 
 namespace blink {
 namespace mojom {
 enum class MediaSessionAction;
 }  // namespace mojom
 }  // namespace blink
 
 namespace content {
 
 class MediaSession;
-class MediaSessionImpl;
 
 // The observer for observing MediaSession events.
 class CONTENT_EXPORT MediaSessionObserver {
  public:
   // Gets the observed MediaSession. Will return null when the session is
   // destroyed.
   MediaSession* media_session() const;
 
   // Called when the observed MediaSession is being destroyed. Give subclass a
   // chance to clean up. media_session() will return nullptr after this method
   // is called.
   virtual void MediaSessionDestroyed() {}
 
   // Called when the observed MediaSession has changed its state.
   virtual void MediaSessionStateChanged(bool is_controllable,
                                         bool is_suspended) {}
 
   // Called when the observed MediaSession has changed metadata.
   virtual void MediaSessionMetadataChanged(
       const base::Optional<MediaMetadata>& metadata) {}
 
   // Called when the media session action list has changed.
   virtual void MediaSessionActionsChanged(
       const std::set<blink::mojom::MediaSessionAction>& action) {}
 
  protected:
   // Create a MediaSessionObserver and start observing a session.
-  MediaSessionObserver(MediaSession* media_session);
+  explicit MediaSessionObserver(MediaSession* media_session);
   // Destruct a MediaSessionObserver and remove it from the session if it's
   // still observing.
   virtual ~MediaSessionObserver();
 
  private:
   friend class MediaSessionImpl;
 
   void StopObserving();
 
   // Weak pointer to MediaSession
-  MediaSessionImpl* media_session_;
+  MediaSession* media_session_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaSessionObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_MEDIA_SESSION_OBSERVER_H_