content: Cleanup class/struct forward declarations

content/common/gamepad_param_traits.h

 // Copyright 2014 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_COMMON_GAMEPAD_PARAM_TRAITS_H_
 #define CONTENT_COMMON_GAMEPAD_PARAM_TRAITS_H_
 
 #include <string>
 
 #include "ipc/ipc_param_traits.h"
 
 namespace base {
 class Pickle;
 class PickleIterator;
 }
 
 namespace blink { class WebGamepad; }
 
 namespace IPC {
 
-class Message;
-
 template <>
 struct ParamTraits<blink::WebGamepad> {
   typedef blink::WebGamepad param_type;
   static void Write(base::Pickle* m, const blink::WebGamepad& p);
   static bool Read(const base::Pickle* m,
                    base::PickleIterator* iter,
                    blink::WebGamepad* p);
   static void Log(const blink::WebGamepad& p, std::string* l);
 };
 
 } // namespace IPC
 
 #endif  // CONTENT_COMMON_GAMEPAD_PARAM_TRAITS_H_