Separate the syncing of extension settings and app settings into separate data

chrome/browser/extensions/extension_settings_observer.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_EXTENSION_SETTINGS_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_
 #pragma once
 
+#include "base/observer_list_threadsafe.h"
 #include "chrome/browser/extensions/extension_setting_changes.h"
 
 class Profile;
 
 // Interface for classes that listen to changes to extension settings.
 class ExtensionSettingsObserver {
  public:
   // Called when a list of settings have changed for an extension.
   //
   // |profile| is the profile of the event originator, or NULL if the event
   // didn't originate from a background page.  This is so that events can avoid
   // being sent back to the background page which made the change.  When the
   // settings API is exposed to content scripts, this will need to be changed.
   virtual void OnSettingsChanged(
       const Profile* profile,
       const std::string& extension_id,
       const ExtensionSettingChanges& changes) = 0;
 
  protected:
   virtual ~ExtensionSettingsObserver();
 };
 
+typedef ObserverListThreadSafe<ExtensionSettingsObserver>
+    ExtensionSettingsObserverList;
+
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_