Implement extension controlled indicators, starting with New Tab page

chrome/browser/resources/settings/on_startup_page/on_startup_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.
 
 /**
  * @fileoverview
  * 'settings-on-startup-page' is a settings page.
  *
  * Example:
  *
  *    <neon-animated-pages>
  *      <settings-on-startup-page prefs="{{prefs}}">
  *      </settings-on-startup-page>
  *      ... other pages ...
  *    </neon-animated-pages>
  */
 Polymer({
   is: 'settings-on-startup-page',
 
   properties: {
-    /**
-     * Preferences state.
-     */
     prefs: {
       type: Object,
       notify: true,
     },
 
+    /** @private {?NtpExtension} */
+    ntpExtension_: Object,
+
     /**
      * Enum values for the 'session.restore_on_startup' preference.
      * @private {!Object<string, number>}
      */
     prefValues_: {
       readOnly: true,
       type: Object,
       value: {
         OPEN_NEW_TAB: 5,

[dpapad, 2016/11/17 01:50:07]

Nit: Alphabetize? Or sort by value?

[Dan Beam, 2016/11/17 02:50:14]

Done.

         CONTINUE: 1,
         OPEN_SPECIFIC: 4,
       },
     },
   },
 
+  attached: function() {

[dpapad, 2016/11/17 01:50:07]

@override

[Dan Beam, 2016/11/17 02:50:14]

Done.

+    this.getNtpExtension_();
+  },
+
+  /** @private */
+  getNtpExtension_: function() {
+    settings.OnStartupBrowserProxyImpl.getInstance().getNtpExtension().then(
+        function(ntpExtension) {
+          this.ntpExtension_ = ntpExtension;
+        }.bind(this));
+  },
+
+  /**
+   * @param {?NtpExtension} ntpExtension
+   * @param {number} restoreOnStartup Value of prefs.session.restore_on_startup.
+   * @return {boolean}
+   * @private
+   */
+  showIndicator_: function(ntpExtension, restoreOnStartup) {
+    return !!ntpExtension && restoreOnStartup == this.prefValues_.OPEN_NEW_TAB;
+  },
+
   /**
     * Determine whether to show the user defined startup pages.
     * @param {number} restoreOnStartup Enum value from prefValues_.
     * @return {boolean} Whether the open specific pages is selected.
     * @private
     */
   showStartupUrls_: function(restoreOnStartup) {
     return restoreOnStartup == this.prefValues_.OPEN_SPECIFIC;
   },
 });