Move Extension into extensions namespace

chrome/browser/extensions/convert_user_script.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_CONVERT_USER_SCRIPT_H_
 #define CHROME_BROWSER_EXTENSIONS_CONVERT_USER_SCRIPT_H_
 #pragma once
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
 #include "base/string16.h"
 
-class Extension;
 class FilePath;
 class GURL;
 
+namespace extensions {
+class Extension;
+}
+
 // Wraps the specified user script in an extension. The extension is created
 // unpacked in the system temp dir. Returns a valid extension that the caller
 // should take ownership on success, or NULL and |error| on failure.
 //
 // NOTE: This function does file IO and should not be called on the UI thread.
 // NOTE: The caller takes ownership of the directory at extension->path() on the
 // returned object.
-scoped_refptr<Extension> ConvertUserScriptToExtension(
+scoped_refptr<extensions::Extension> ConvertUserScriptToExtension(
     const FilePath& user_script, const GURL& original_url, string16* error);
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CONVERT_USER_SCRIPT_H_