Move Extension into extensions namespace

chrome/browser/background/background_mode_manager_aura.cc

 // 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.
 
 #include "chrome/browser/background/background_mode_manager.h"
 
+#include "chrome/common/extensions/extension.h"
 #include "grit/generated_resources.h"
 #include "ui/base/l10n/l10n_util.h"
 
 // No background jobs for aura for now.
 
 void BackgroundModeManager::EnableLaunchOnStartup(bool should_launch) {
   NOTIMPLEMENTED();
 }
 
 void BackgroundModeManager::DisplayAppInstalledNotification(
-    const Extension* extension) {
+    const extensions::Extension* extension) {
   NOTIMPLEMENTED();
 }
 
 string16 BackgroundModeManager::GetPreferencesMenuLabel() {
   return l10n_util::GetStringUTF16(IDS_SETTINGS);
 }