ChromeOS: Implement Accessibility Options screen of material design OOBE.

chrome/browser/resources/chromeos/login/oobe_a11y_option.js

 // Copyright 2016 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.
 
 Polymer({
-  is: 'oobe-dialog',
+  is: 'oobe-a11y-option',
 
   properties: {
     /**
-     * Controls visibility of the bottom-buttons element.
+     * If paper-toggle-button is checked.
      */
-    hasButtons: {
+    checked: {
       type: Boolean,
-      value: false,
+    },
+
+    /**
+     * Chrome message handling this option.
+     */
+    chromeMessage: {
+      type: String,
     },
   },
 });