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

ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_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-checkbox` is a button that can be either checked or unchecked. User
  * can tap the checkbox to check or uncheck it. Usually you use checkboxes
  * to allow user to select multiple options from a set. If you have a single
  * ON/OFF option, avoid using a single checkbox and use `cr-toggle-button`
  * instead.
  *
  * Example:
  *     <cr-checkbox></cr-checkbox>
  *     <cr-checkbox checked></cr-checkbox>
  *
  * @element cr-checkbox
  */
 Polymer({
   is: 'cr-checkbox',
 
   properties: {
     /**
      * Gets or sets the state. `true` is checked and `false` is unchecked.
-     *
-     * @attribute checked
-     * @type {boolean}
-     * @default false
      */
     checked: {
       type: Boolean,
       value: false,
+      notify: true,
       reflectToAttribute: true
     },
 
     /**
      * If true, the user cannot interact with this element.
-     *
-     * @attribute disabled
-     * @type {boolean}
-     * @default false
      */
     disabled: {
       type: Boolean,
       value: false,
       reflectToAttribute: true
     },
   },
 
   toggle: function() {
     this.$.checkbox.toggle();
   },
 });