MD History: Add lazy-render element for simple lazy initialization.

chrome/browser/resources/md_history/synced_device_manager.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.
 
 /**
  * @typedef {{device: string,
  *           lastUpdateTime: string,
  *           separatorIndexes: !Array<number>,
  *           timestamp: number,
  *           tabs: !Array<!ForeignSessionTab>,
@@ skipping 100 matching lines @@
       tag: session.tag,
     };
   },
 
   onSignInTap_: function() {
     chrome.send('SyncSetupShowSetupUI');
     chrome.send('SyncSetupStartSignIn', [false]);
   },
 
   onToggleMenu_: function(e) {
-    this.$.menu.toggleMenu(e.detail.target, e.detail.tag);
+    this.$.menu.get().then(function(menu) {
+      menu.toggleMenu(e.detail.target, e.detail.tag);
+    });
   },
 
   onOpenAllTap_: function() {
+    var menu = assert(this.$.menu.getIfExists());
     md_history.BrowserService.getInstance().openForeignSessionAllTabs(
-        this.$.menu.itemData);
-    this.$.menu.closeMenu();
+        menu.itemData);
+    menu.closeMenu();
   },
 
   onDeleteSessionTap_: function() {
+    var menu = assert(this.$.menu.getIfExists());
     md_history.BrowserService.getInstance().deleteForeignSession(
-        this.$.menu.itemData);
-    this.$.menu.closeMenu();
+        menu.itemData);
+    menu.closeMenu();
   },
 
   /** @private */
   clearDisplayedSyncedDevices_: function() {
     this.syncedDevices_ = [];
   },
 
   /**
    * Decide whether or not should display no synced tabs message.
    * @param {boolean} signInState
@@ skipping 92 matching lines @@
     // User signed in, show the loading message when querying for synced
     // devices.
     this.fetchingSyncedTabs_ = true;
   },
 
   searchTermChanged: function(searchTerm) {
     this.clearDisplayedSyncedDevices_();
     this.updateSyncedDevices(this.sessionList);
   }
 });