chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/instant_ui.h

 // Copyright (c) 2012 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_UI_WEBUI_INSTANT_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_INSTANT_UI_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_ui_controller.h"
 
-
-namespace content {
-class BrowserContext;
-}
-
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 // Provides configuration options for Instant web search and shows debug info.
 class InstantUI : public content::WebUIController {
  public:
   // Constructs an instance using |web_ui| for its data sources and message
   // handlers.
   explicit InstantUI(content::WebUI* web_ui);
 
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InstantUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_INSTANT_UI_H_