Lazy init prefs in 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}}"
  *          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: {
       type: Object,
       notify: true,
-      value: null
     },
 
     inverted: {
       type: Boolean,
       value: false
     },
 
     checked: {
       type: Boolean,
       value: false,
@@ skipping 15 matching lines @@
     'prefValueChanged_(pref.value)'
   ],
 
   /** @override */
   ready: function() {
     this.$.events.forward(this.$.checkbox, ['change']);
   },
 
   /** @private */
   prefValueChanged_: function(prefValue) {
-    // prefValue is initially undefined when Polymer initializes pref.
-    if (prefValue !== undefined) {
-      this.checked = this.getNewValue_(prefValue);
-    }
+    this.checked = this.getNewValue_(prefValue);
   },
 
   /** @private */
   checkedChanged_: function() {
     if (this.pref) {
       this.set('pref.value', this.getNewValue_(this.checked));
     }
   },
 
   /** @private */
   getNewValue_: function(val) {
     return this.inverted ? !val : val;
   }
 });