Add onChanged events to the extension settings API, both from sync and between

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 "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();
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_