extensions: Cleanup class/struct fwd declarations

extensions/renderer/v8_context_native_handler.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_V8_CONTEXT_NATIVE_HANDLER_H_
 #define EXTENSIONS_RENDERER_V8_CONTEXT_NATIVE_HANDLER_H_
 
 #include "extensions/renderer/object_backed_native_handler.h"
 
 namespace extensions {
 
-class Dispatcher;
-
 class V8ContextNativeHandler : public ObjectBackedNativeHandler {
  public:
   explicit V8ContextNativeHandler(ScriptContext* context);
 
  private:
   void GetAvailability(const v8::FunctionCallbackInfo<v8::Value>& args);
   void GetModuleSystem(const v8::FunctionCallbackInfo<v8::Value>& args);
 
   ScriptContext* context_;
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_V8_CONTEXT_NATIVE_HANDLER_H_