Cleanup: Remove unneeded forward declarations from chrome/browser/extensions.

chrome/browser/extensions/extension_message_handler.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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_HANDLER_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_HANDLER_H_
 #pragma once
 
+#include <string>
+
 #include "content/browser/renderer_host/render_view_host_observer.h"
 
-class Profile;
-struct ExtensionHostMsg_DomMessage_Params;
-
 // Filters and dispatches extension-related IPC messages that arrive from
 // renderers. There is one of these objects for each RenderViewHost in Chrome.
 // Contrast this with ExtensionTabHelper, which is only created for TabContents.
 //
 // TODO(aa): Handling of content script messaging should be able to move to EFD
 // once there is an EFD for every RVHD where extension code can run. Then we
 // could eliminate this class. Right now, we don't end up with an EFD for tab
 // contents unless that tab contents is hosting chrome-extension:// URLs. That
 // still leaves content scripts. See also: crbug.com/80307.
 class ExtensionMessageHandler : public RenderViewHostObserver {
  public:
   // |sender| is guaranteed to outlive this object.
   explicit ExtensionMessageHandler(RenderViewHost* render_view_host);
   virtual ~ExtensionMessageHandler();
 
   // RenderViewHostObserver overrides.
   virtual void RenderViewHostInitialized() OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
  private:
   // Message handlers.
   void OnPostMessage(int port_id, const std::string& message);
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionMessageHandler);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_HANDLER_H_