Refactor prefs.js for MD-Settings

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}}"
@@ skipping 50 matching lines @@
   prefValueChanged_: function(prefValue) {
     // prefValue is initially undefined when Polymer initializes pref.
     if (prefValue !== undefined) {
       this.checked = this.getNewValue_(prefValue);
     }
   },
 
   /** @private */
   checkedChanged_: function() {
     if (this.pref) {
-      this.pref.value = this.getNewValue_(this.checked);
+      this.set('pref.value', this.getNewValue_(this.checked));
     }
   },
 
   /** @private */
   getNewValue_: function(val) {
     return this.inverted ? !val : val;
   }
 });