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.
 
 Polymer({
   is: 'history-app',
 
   behaviors: [Polymer.IronScrollTargetBehavior],
 
   properties: {
@@ skipping 45 matching lines @@
     routeData_: Object,
 
     // The query params for the page.
     queryParams_: Object,
 
     // True if the window is narrow enough for the page to have a drawer.
     hasDrawer_: Boolean,
 
     isUserSignedIn_: {
       type: Boolean,
-      // Updated on synced-device-manager attach by chrome.sending
-      // 'otherDevicesInitialized'.
+      // Updated on synced-device-manager.
       value: loadTimeData.getBoolean('isUserSignedIn'),
     },
 
     toolbarShadow_: {
       type: Boolean,
       reflectToAttribute: true,
       notify: true,
     }
   },
 
@@ skipping 292 matching lines @@
             break;
         }
         break;
     }
 
     md_history.BrowserService.getInstance().recordHistogram(
       'History.HistoryPageView', histogramValue, HistoryPageViewHistogram.END
     );
   },
 });