Move Extension into extensions namespace

chrome/browser/extensions/extension_install_dialog.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_INSTALL_DIALOG_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_INSTALL_DIALOG_H_
 #pragma once
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
 #include "base/string16.h"
 #include "chrome/browser/extensions/extension_install_ui.h"
 
-class Extension;
 class Profile;
 class SkBitmap;
 
 namespace base {
 class DictionaryValue;
 }
 
 void ShowExtensionInstallDialog(Profile* profile,
                                 ExtensionInstallUI::Delegate* delegate,
                                 const ExtensionInstallUI::Prompt& prompt);
 
 // The implementations of this function are platform-specific.
 void ShowExtensionInstallDialogImpl(Profile* profile,
                                     ExtensionInstallUI::Delegate* delegate,
                                     const ExtensionInstallUI::Prompt& prompt);
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_INSTALL_DIALOG_H_