content: Cleanup class/struct forward declarations

content/browser/media/session/pepper_player_delegate.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_BROWSER_MEDIA_SESSION_PEPPER_PLAYER_DELEGATE_H_
 #define CONTENT_BROWSER_MEDIA_SESSION_PEPPER_PLAYER_DELEGATE_H_
 
 #include "base/macros.h"
 #include "content/browser/media/session/media_session_player_observer.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 
 namespace content {
 
-class PepperWebContentsObserver;
-
 class PepperPlayerDelegate : public MediaSessionPlayerObserver {
  public:
   // The Id can only be 0 for PepperPlayerDelegate. Declare the constant here so
   // it can be used elsewhere.
   static const int kPlayerId;
 
   PepperPlayerDelegate(
       WebContentsImpl* contents, int32_t pp_instance);
   ~PepperPlayerDelegate() override;
 
   // MediaSessionPlayerObserver implementation.
   void OnSuspend(int player_id) override;
   void OnResume(int player_id) override;
   void OnSetVolumeMultiplier(int player_id,
                              double volume_multiplier) override;
 
  private:
   void SetVolume(int player_id, double volume);
 
   WebContentsImpl* contents_;
   int32_t pp_instance_;
 
   DISALLOW_COPY_AND_ASSIGN(PepperPlayerDelegate);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_SESSION_PEPPER_PLAYER_DELEGATE_H_