MD History: Update sign in state in data source

chrome/browser/resources/md_history/app.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.
 
 cr.define('md_history', function() {
   var lazyLoadPromise = null;
   function ensureLazyLoaded() {
     if (!lazyLoadPromise) {
       lazyLoadPromise = new Promise(function(resolve, reject) {
         Polymer.Base.importHref(
             'chrome://history/lazy_load.html', resolve, reject, true);
       });
     }
     return lazyLoadPromise;
   }
 
   return {
     ensureLazyLoaded: ensureLazyLoaded,
   };
 });
 
 Polymer({
   is: 'history-app',
 
-  behaviors: [Polymer.IronScrollTargetBehavior],
+  behaviors: [
+    Polymer.IronScrollTargetBehavior,
+    WebUIListenerBehavior,
+  ],
 
   properties: {
     // Used to display notices for profile sign-in status.
     showSidebarFooter: Boolean,
 
     hasSyncedResults: Boolean,
 
     // The id of the currently selected page.
     selectedPage_: {type: String, observer: 'selectedPageChanged_'},
 
@@ skipping 62 matching lines @@
 
   /** @override */
   ready: function() {
     this.grouped_ = loadTimeData.getBoolean('groupByDomain');
 
     cr.ui.decorate('command', cr.ui.Command);
     document.addEventListener('canExecute', this.onCanExecute_.bind(this));
     document.addEventListener('command', this.onCommand_.bind(this));
   },
 
+  /** @override */
+  attached: function() {
+    this.addWebUIListener('sign-in-state-updated',
+                          this.updateSignInState.bind(this));
+  },
+
   onFirstRender: function() {
     setTimeout(function() {
       chrome.send(
           'metricsHandler:recordTime',
           ['History.ResultsRenderedTime', window.performance.now()]);
     });
 
     // Focus the search field on load. Done here to ensure the history page
     // is rendered before we try to take focus.
     var searchField =
@@ skipping 223 matching lines @@
             break;
         }
         break;
     }
 
     md_history.BrowserService.getInstance().recordHistogram(
       'History.HistoryPageView', histogramValue, HistoryPageViewHistogram.END
     );
   },
 });