chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/extension_disabled_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_EXTENSIONS_EXTENSION_DISABLED_UI_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_DISABLED_UI_H_
 
 class ExtensionService;
-namespace content {
-class WebContents;
-}
 
 namespace extensions {
 
 class Extension;
 
 // Adds a global error to inform the user that an extension was
 // disabled after upgrading to higher permissions.
 // If |is_remote_install| is true, the extension was disabled because
 // it was installed remotely.
 void AddExtensionDisabledError(ExtensionService* service,
                                const Extension* extension,
                                bool is_remote_install);
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_DISABLED_UI_H_