Fix the pref binding by binding to the object rather than the element

chrome/browser/resources/settings/checkbox/checkbox.js

 // 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.
 
 /**
  * @fileoverview
  * `cr-settings-checkbox` is a checkbox that controls a supplied preference.
  *
  * Example:
  *      <cr-settings-checkbox pref="{{prefs.settings.enableFoo}}"
  *          label="Enable foo setting." subLabel="(bar also)">
  *      </cr-settings-checkbox>
  *
  * @element cr-settings-checkbox
  */
 Polymer({
   is: 'cr-settings-checkbox',
 
   properties: {
     /**
      * The boolean preference object to control.
      * @type {?chrome.settingsPrivate.PrefObject}
      */
-    pref: Object,
+    pref: {
+      type: Object,
+      notify: true,
+    },
 
     label: {
       type: String,
       value: '',
     },
 
     subLabel: {
       type: String,
       value: '',
     },
   },
 
   /** @override */
   ready: function() {
     this.$.events.forward(this.$.checkbox, ['change']);
   },
 });