Add cr-checkbox to Chrome

ui/webui/resources/cr_elements/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-toggle-button` provides a switch the user can toggle on or off by
- * tapping or by dragging. Wraps a `paper-toggle-button`.
+ * `paper-checkbox` is a button that can be either checked or unchecked.  User

[michaelpg, 2015/02/11 02:08:10]

cr-checkbox, cr-toggle-button, etc

[Oren Blasberg, 2015/02/11 20:12:42]

Done.

+ * 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 `paper-toggle-button`
+ * instead.
  *
  * Example:
+ *     <paper-checkbox></paper-checkbox>

[Jeremy Klein, 2015/02/11 01:55:36]

cr-checkbox

[Oren Blasberg, 2015/02/11 20:12:42]

Done.

+ *     <paper-checkbox checked></paper-checkbox>
  *
- *    <cr-toggle-button></cr-toggle-button>
- *
- * @element cr-toggle-button
+ * @element cr-checkbox
  */
 Polymer({

[Jeremy Klein, 2015/02/11 01:55:36]

Should we also expose the toggle function?

[Oren Blasberg, 2015/02/11 20:12:42]

Done.

   publish: {
     /**
      * Gets or sets the state. `true` is checked and `false` is unchecked.
      *
      * @attribute checked
      * @type boolean
      * @default false
      */
     checked: {
       value: false,
       reflect: true,
     },
 
 
     /**
+     * The label for the checkbox.
+     *
+     * @attribute label
+     * @type string
+     * @default ''
+     */
+    label: '',
+
+
+    /**
      * If true, the toggle button is disabled.
      *
      * @attribute disabled
      * @type boolean
      * @default false
      */
     disabled: {
       value: false,
       reflect: true,
     },
   },
 
   ready: function() {
     this.$.events.forward(this.$.button, ['change']);
   },
 });