[Blink>MediaSession] Use setActionCallback() instead of event listeners for media control actions

third_party/WebKit/Source/modules/mediasession/NavigatorMediaSession.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 NavigatorMediaSession_h
 #define NavigatorMediaSession_h
 
 #include "core/frame/Navigator.h"
 #include "modules/mediasession/MediaSession.h"
 #include "platform/Supplementable.h"
 
 namespace blink {
 
 class Navigator;
+class ScriptState;
 
 // Provides MediaSession as a supplement of Navigator as an attribute.
 class NavigatorMediaSession final
     : public GarbageCollected<NavigatorMediaSession>,
       public Supplement<Navigator> {
   USING_GARBAGE_COLLECTED_MIXIN(NavigatorMediaSession);
 
  public:
   static NavigatorMediaSession& from(Navigator&);
   static MediaSession* mediaSession(ScriptState*, Navigator&);
 
   DECLARE_TRACE();
 
  private:
   NavigatorMediaSession(Navigator&);
   static const char* supplementName();
 
   // The MediaSession instance of this Navigator.
   Member<MediaSession> m_session;
 };
 
 }  // namespace blink
 
 #endif  // NavigatorMediaSession_h