MD History: fix script errors when navigating to /syncedTabs (or refreshing)

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,
-    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 72 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 116 matching lines @@
   /**
    * @param {!Array<!ForeignSession>} sessionList Array of objects describing
    *     the sessions from other devices.
    * @param {boolean} isTabSyncEnabled Is tab sync enabled for this profile?
    */
   setForeignSessions: function(sessionList, isTabSyncEnabled) {
     if (!isTabSyncEnabled) {
       var syncedDeviceManagerElem =
       /** @type {HistorySyncedDeviceManagerElement} */this
           .$$('history-synced-device-manager');
-      if (syncedDeviceManagerElem)
-        syncedDeviceManagerElem.tabSyncDisabled();
+      if (syncedDeviceManagerElem) {
+        md_history.ensureLazyLoaded().then(function() {
+          syncedDeviceManagerElem.tabSyncDisabled();
+        });
+      }
       return;
     }
 
     this.set('queryResult_.sessionList', sessionList);
   },
 
   /**
    * Called when browsing data is cleared.
    */
   historyDeleted: function() {
@@ skipping 45 matching lines @@
   selectedPageChanged_: function() {
     this.unselectAll();
     this.historyViewChanged_();
   },
 
   /** @private */
   historyViewChanged_: function() {
     // This allows the synced-device-manager to render so that it can be set as
     // the scroll target.
     requestAnimationFrame(function() {
-      // <iron-pages> can occasionally end up with no item selected during
-      // tests.
-      if (!this.$.content.selectedItem)
-        return;
-      this.scrollTarget =
-          this.$.content.selectedItem.getContentScrollTarget();
-      this._scrollHandler();
+      md_history.ensureLazyLoaded().then(function() {
+        // <iron-pages> can occasionally end up with no item selected during
+        // tests.
+        if (!this.$.content.selectedItem)
+          return;
+        this.scrollTarget =
+            this.$.content.selectedItem.getContentScrollTarget();
+        this._scrollHandler();
+      }.bind(this));
     }.bind(this));
     this.recordHistoryPageView_();
   },
 
   /**
    * This computed binding is needed to make the iron-pages selector update when
    * the synced-device-manager is instantiated for the first time. Otherwise the
    * fallback selection will continue to be used after the corresponding item is
    * added as a child of iron-pages.
    * @param {string} selectedPage
@@ skipping 32 matching lines @@
             break;
         }
         break;
     }
 
     md_history.BrowserService.getInstance().recordHistogram(
       'History.HistoryPageView', histogramValue, HistoryPageViewHistogram.END
     );
   },
 });