cr-settings-checkbox: Add 'inverted' property.

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,
+      notify: true
+    },
+
+    inverted: {
+      type: Boolean,
+      value: false
+    },
+
+    checked: {
+      type: Boolean,
+      value: false,
+      observer: 'checkedChanged_'
     },
 
     label: {
       type: String,
       value: '',
     },
 
     subLabel: {
       type: String,
       value: '',
     },
   },
 
+  observers: [
+    '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);
+    }
+  },
+
+  /** @private */
+  checkedChanged_: function() {
+    if (this.pref) {
+      this.pref.value = this.getNewValue_(this.checked);
+    }
+  },
+
+  /** @private */
+  getNewValue_: function(val) {
+    return this.inverted ? !val : val;
+  }
 });