chrome.settingsPrivate: Implement onPrefsChanged event handling.

chrome/common/extensions/api/settings_private.idl

 // Copyright 2015 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.
 
 // Use the <code>chrome.settingsPrivate</code> API to get or set preferences
 // from the settings UI.
 namespace settingsPrivate {
   // Type of a pref.
   enum PrefType { BOOLEAN, NUMBER, STRING, URL, LIST };
 
@@ skipping 38 matching lines @@
     // Gets an array of all the prefs.
     static void getAllPrefs(GetAllPrefsCallback callback);
 
     // Gets the value of a specific pref.
     static void getPref(DOMString name, GetPrefCallback callback);
   };
 
   interface Events {
     // Fired when a set of prefs has changed.
     //
-    // |callback|: Callback fired with a list of prefs that changed.
-    static void onPrefsChanged(GetAllPrefsCallback callback);
+    // |prefs| The prefs that changed.
+    static void onPrefsChanged(PrefObject[] prefs);
   };
 };