[MD settings] adding isNewTabPage setting radio buttons

chrome/browser/resources/settings/appearance_page/appearance_page.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.
 
-
-
 /**
  * 'cr-settings-appearance-page' is the settings page containing appearance
  * settings.
  *
  * Example:
  *
  *    <iron-animated-pages>
  *      <cr-settings-appearance-page prefs="{{prefs}}">
  *      </cr-settings-appearance-page>
  *      ... other pages ...
  *    </iron-animated-pages>
  *
  * @group Chrome Settings Elements
  * @element cr-settings-appearance-page
  */
 Polymer({
   is: 'cr-settings-appearance-page',
 
+  properties: {
+    /**
+     * Preferences state.
+     */
+    prefs: {
+      type: Object,
+      notify: true,
+    },
+
+    // prefs.homepage_is_newtabpage.value
+    isNewTabPageString_: {
+      type: String,
+      notify: true,
+      observer: 'isNewTabPageStringChanged_',
+    }
+  },
+
+  observers: [
+    'homepageIsNewTabPageChanged_(prefs.homepage_is_newtabpage.value)',
+  ],
+
   /** @override */
   attached: function() {
     // Query the initial state.
     cr.sendWithCallback('getResetThemeEnabled', undefined,
                         this.setResetThemeEnabled.bind(this));
 
     // Set up the change event listener.
     cr.addWebUIListener('reset-theme-enabled-changed',
                         this.setResetThemeEnabled.bind(this));
   },
 
-  properties: {
-    /**
-     * Preferences state.
-     */
-    prefs: {
-      type: Object,
-      notify: true,
-    },
+  /** @private */
+  homepageIsNewTabPageChanged_: function(newValue) {
+    this.isNewTabPageString_ = (newValue == true).toString();
+  },
+
+  /** @private */
+  isNewTabPageStringChanged_: function(newValue) {
+    this.set('prefs.homepage_is_newtabpage.value',
+        this.isNewTabPageString_ == 'true');
   },
 
   setResetThemeEnabled: function(enabled) {
     this.$.resetTheme.disabled = !enabled;
   },
 
   /** @private */
   openThemesGallery_: function() {
     window.open(loadTimeData.getString('themesGalleryUrl'));
   },
 
   /** @private */
   resetTheme_: function() {
     chrome.send('resetTheme');
   },
 });