extensions: Cleanup class/struct fwd declarations

extensions/common/permissions/api_permission.h

 // Copyright 2013 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 EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_H_
 #define EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_H_
 
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/pickle.h"
 #include "base/values.h"
 
-namespace IPC {
-class Message;
-}
-
 namespace extensions {
 
 class PermissionIDSet;
 class APIPermissionInfo;
 class ChromeAPIPermissions;
 
 // APIPermission is for handling some complex permissions. Please refer to
 // extensions::SocketPermission as an example.
 // There is one instance per permission per loaded extension.
 class APIPermission {
@@ skipping 403 matching lines @@
 
   const APIPermission::ID id_;
   const char* const name_;
   const int flags_;
   const APIPermissionConstructor api_permission_constructor_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_PERMISSIONS_API_PERMISSION_H_