Add a 0.8 version of cr-checkbox with a demo

ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_checkbox.js

Index: ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_checkbox.js
diff --git a/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.js b/ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_checkbox.js
similarity index 72%
copy from ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.js
copy to ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_checkbox.js
index 3c53b64faaa7c31654f5957dd2d26c8857d758a8..dcf12a0d4ff53499e7f9be39852abdf3972d69e4 100644
--- a/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.js
+++ b/ui/webui/resources/cr_elements/v0_8/cr_checkbox/cr_checkbox.js
@@ -17,40 +17,37 @@
  * @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']);
-  },
 });