Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/session/media_session_observer.h

 // Copyright 2015 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_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_OBSERVER_H_
-#define CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_OBSERVER_H_
+#ifndef CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_OBSERVER_H_
+#define CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_OBSERVER_H_
 
 namespace content {
 
 class MediaSessionObserver {
  public:
   MediaSessionObserver() = default;
   virtual ~MediaSessionObserver() = default;
 
   // The given |player_id| has been suspended by the MediaSession.
   virtual void OnSuspend(int player_id) = 0;
 
   // The given |player_id| has been resumed by the MediaSession.
   virtual void OnResume(int player_id) = 0;
 
   // The given |player_id| has been set a new volume multiplier by
   // the MediaSession.
   virtual void OnSetVolumeMultiplier(int player_id,
                                      double volume_multiplier) = 0;
 };
 
 }  // namespace content
 
-#endif // CONTENT_BROWSER_MEDIA_ANDROID_MEDIA_SESSION_OBSERVER_H_
+#endif // CONTENT_BROWSER_MEDIA_SESSION_MEDIA_SESSION_OBSERVER_H_