Move Extension into extensions namespace

chrome/browser/background/background_mode_manager_mac.mm

 // 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 "base/bind.h"
 #include "base/command_line.h"
 #include "base/mac/mac_util.h"
 #include "chrome/browser/background/background_mode_manager.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/prefs/pref_service.h"
@@ skipping 56 matching lines @@
       return;
     }
     // Call to the File thread to remove the login item since it requires
     // accessing the disk.
     BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE,
                             base::Bind(DisableLaunchOnStartupCallback));
   }
 }
 
 void BackgroundModeManager::DisplayAppInstalledNotification(
-    const Extension* extension) {
+    const extensions::Extension* extension) {
   // TODO(atwilson): Display a platform-appropriate notification here.
   // http://crbug.com/74970
 }
 
 string16 BackgroundModeManager::GetPreferencesMenuLabel() {
   return l10n_util::GetStringUTF16(IDS_OPTIONS);
 }