MD Bookmarks: Lazily render dropdown menus

chrome/test/data/webui/md_bookmarks/command_manager_test.js

 // Copyright 2017 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.
 
 suite('<bookmarks-command-manager>', function() {
   var commandManager;
   var store;
   var lastCommand;
   var lastCommandIds;
 
@@ skipping 32 matching lines @@
               [
                 createFolder('21', []),
               ]))
     });
     store.replaceSingleton();
 
     commandManager = new TestCommandManager();
     replaceBody(commandManager);
     document.body.appendChild(
         document.createElement('bookmarks-toast-manager'));
-
-    Polymer.dom.flush();
   });
 
   test('can only copy single URL items', function() {
     assertFalse(commandManager.canExecute(Command.COPY, new Set(['11'])));
     assertFalse(commandManager.canExecute(Command.COPY, new Set(['11', '13'])));
     assertTrue(commandManager.canExecute(Command.COPY, new Set(['13'])));
   });
 
   test('context menu hides invalid commands', function() {
     store.data.selection.items = new Set(['11', '13']);
     store.notifyObservers();
 
     commandManager.openCommandMenuAtPosition(0, 0);
+    Polymer.dom.flush();
+
     var commandHidden = {};
     commandManager.root.querySelectorAll('.dropdown-item').forEach(element => {
       commandHidden[element.getAttribute('command')] = element.hidden;
     });
 
     // With a folder and an item selected, the only available context menu item
     // is 'Delete'.
     assertTrue(commandHidden['edit']);
     assertTrue(commandHidden['copy']);
     assertFalse(commandHidden['delete']);
@@ skipping 103 matching lines @@
     commandManager.assertLastCommand(Command.OPEN_NEW_WINDOW);
   });
 
   test('cannot execute "Open in New Tab" on folders with no items', function() {
     var items = new Set(['2']);
     assertFalse(commandManager.canExecute(Command.OPEN_NEW_TAB, items));
 
     store.data.selection.items = items;
 
     commandManager.openCommandMenuAtPosition(0, 0);
+    Polymer.dom.flush();
+
     var commandItem = {};
     commandManager.root.querySelectorAll('.dropdown-item').forEach(element => {
       commandItem[element.getAttribute('command')] = element;
     });
 
     assertTrue(commandItem[Command.OPEN_NEW_TAB].disabled);
     assertFalse(commandItem[Command.OPEN_NEW_TAB].hidden);
 
     assertTrue(commandItem[Command.OPEN_NEW_WINDOW].disabled);
     assertFalse(commandItem[Command.OPEN_NEW_WINDOW].hidden);
@@ skipping 105 matching lines @@
     assertOpenedTabs(['http://111/', 'http://12/']);
   });
 
   test('control-double click opens full selection', function() {
     customClick(items[0]);
     simulateDoubleClick(items[2], {ctrlKey: true});
 
     assertOpenedTabs(['http://111/', 'http://13/']);
   });
 });