extensions: Cleanup class/struct fwd declarations

extensions/renderer/script_injection_manager.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 EXTENSIONS_RENDERER_SCRIPT_INJECTION_MANAGER_H_
 #define EXTENSIONS_RENDERER_SCRIPT_INJECTION_MANAGER_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/scoped_observer.h"
 #include "extensions/common/user_script.h"
 #include "extensions/renderer/script_injection.h"
 #include "extensions/renderer/user_script_set_manager.h"
 
 struct ExtensionMsg_ExecuteCode_Params;
 
 namespace content {
 class RenderFrame;
 }
 
 namespace extensions {
-class Extension;
 
 // The ScriptInjectionManager manages extensions injecting scripts into frames
 // via both content/user scripts and tabs.executeScript(). It is responsible for
 // maintaining any pending injections awaiting permission or the appropriate
 // load point, and injecting them when ready.
 class ScriptInjectionManager : public UserScriptSetManager::Observer {
  public:
   explicit ScriptInjectionManager(
       UserScriptSetManager* user_script_set_manager);
   virtual ~ScriptInjectionManager();
@@ skipping 83 matching lines @@
 
   ScopedObserver<UserScriptSetManager, UserScriptSetManager::Observer>
       user_script_set_manager_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ScriptInjectionManager);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_SCRIPT_INJECTION_MANAGER_H_