Add a 0.8 version of cr-checkbox with a demo

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({
-  publish: {
+  is: 'cr-checkbox',
+
+  properties: {
     /**
      * Gets or sets the state. `true` is checked and `false` is unchecked.
      *
      * @attribute checked
-     * @type boolean
+     * @type {boolean}
      * @default false
      */
-    checked: {value: false, reflect: true},
-
-    /**
-     * The label for the checkbox.
-     *
-     * @attribute label
-     * @type string
-     * @default ''
-     */
-    label: '',
+    checked: {
+      type: Boolean,
+      value: false,
+      reflectToAttribute: true
+    },
 
     /**
      * If true, the user cannot interact with this element.
      *
      * @attribute disabled
-     * @type boolean
+     * @type {boolean}
      * @default false
      */
-    disabled: {value: false, reflect: true},
+    disabled: {
+      type: Boolean,
+      value: false,
+      reflectToAttribute: true
+    },
   },
 
   toggle: function() {
     this.$.checkbox.toggle();
   },
-
-  ready: function() {
-    this.$.events.forward(this.$.checkbox, ['change']);

[Jeremy Klein, 2015/04/24 03:27:42]

Got rid of this because it's never actually fired at the moment. I also sent
out:

https://github.com/PolymerElements/paper-checkbox/pull/6

to fix that. I'll add a 0.8 cr-events in another CL.

-  },
 });