Forward declare v8::Extension in chrome/renderer/extensions/*.

chrome/renderer/extensions/extension_process_bindings.h

 // Copyright (c) 2011 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.
 
 // Exposes extension APIs into the extension process.
 
 #ifndef CHROME_RENDERER_EXTENSIONS_EXTENSION_PROCESS_BINDINGS_H_
 #define CHROME_RENDERER_EXTENSIONS_EXTENSION_PROCESS_BINDINGS_H_
 #pragma once
 
 #include <set>
 #include <string>
 #include <vector>
 
-#include "v8/include/v8.h"
-
 class ExtensionRendererContext;
 class GURL;
 class URLPattern;
 
 namespace WebKit {
 class WebView;
 }
 
+namespace v8 {
+class Extension;
+}
+
 class ExtensionProcessBindings {
  public:
   static v8::Extension* Get(
       ExtensionRendererContext* extension_renderer_context);
 
   // Handles a response to an API request.
   static void HandleResponse(int request_id, bool success,
                              const std::string& response,
                              const std::string& error);
 };
 
 #endif  // CHROME_RENDERER_EXTENSIONS_EXTENSION_PROCESS_BINDINGS_H_