MD User Manager: Fixes flaky tests

chrome/test/data/webui/md_user_manager/control_bar_tests.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('user_manager.control_bar_tests', function() {
   /** @return {!ControlBarElement} */
   function createElement() {
-    PolymerTest.clearBody();
     var controlBarElement = document.createElement('control-bar');
     document.body.appendChild(controlBarElement);
     return controlBarElement;
   }
 
   function registerTests() {
     /** @type {?TestProfileBrowserProxy} */
     var browserProxy = null;
 
     /** @type {?ControlBarElement} */
     var controlBarElement = null;
 
     suite('ControlBarTests', function() {
       setup(function() {
         browserProxy = new TestProfileBrowserProxy();
         // Replace real proxy with mock proxy.
         signin.ProfileBrowserProxyImpl.instance_ = browserProxy;
 
         controlBarElement = createElement();
       });
 
-      teardown(function() { controlBarElement.remove(); });
+      teardown(function(done) {
+        controlBarElement.remove();
+        // Allow asynchronous tasks to finish.
+        setTimeout(done);
+      });
 
       test('Actions are hidden by default', function() {
         assertTrue(controlBarElement.$.launchGuest.hidden);
         assertTrue(controlBarElement.$.addUser.hidden);
 
         controlBarElement.showGuest = true;
         controlBarElement.showAddPerson = true;
         Polymer.dom.flush();
 
         assertFalse(controlBarElement.$.launchGuest.hidden);
@@ skipping 26 matching lines @@
 
       setup(function() {
         browserProxy = new TestProfileBrowserProxy();
         // Replace real proxy with mock proxy.
         signin.ProfileBrowserProxyImpl.instance_ = browserProxy;
 
         browserProxy.setAllProfilesLocked(true);
 
         controlBarElement = createElement();
 
-        errorDialogElement = document.createElement('error-dialog');
-        document.body.appendChild(errorDialogElement);
+        errorDialogElement = document.querySelector('error-dialog');
       });
 
-      teardown(function() {
+      teardown(function(done) {
         controlBarElement.remove();
-        errorDialogElement.remove();
+        // Allow asynchronous tasks to finish.
+        setTimeout(done);
       });
 
       test('Cannot create profile', function() {
         // Simulate clicking 'Create Profile'.
         MockInteractions.tap(controlBarElement.$.addUser);
 
         return browserProxy.whenCalled('areAllProfilesLocked').then(function() {
           // Make sure DOM is up to date.
           Polymer.dom.flush();
 
@@ skipping 14 matching lines @@
           assertLT(0, errorDialogElement.$$('#backdrop').offsetHeight);
         });
       });
     });
   }
 
   return {
     registerTests: registerTests,
   };
 });