MD User Manager: Fixes flaky tests

chrome/test/data/webui/md_user_manager/user_manager_pages_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.user_manager_pages_tests', function() {
   function registerTests() {
     suite('UserManagerPagesTests', function() {
       /** @type {?UserManagerPagesElement} */
       var pagesElement = null;
 
       setup(function() {
-        PolymerTest.clearBody();
         pagesElement = document.createElement('user-manager-pages');
         document.body.appendChild(pagesElement);
       });
 
-      teardown(function() { pagesElement.remove(); });
+      teardown(function(done) {
+        pagesElement.remove();
+        // Allow asynchronous tasks to finish.
+        setTimeout(done);
+      });
 
       test('User Pods page is the default visible page', function() {
         assertTrue(
           pagesElement.isPageVisible_(pagesElement.selectedPage_,
                                       'user-pods-page'));
         assertFalse(
           pagesElement.isPageVisible_(pagesElement.selectedPage_,
                                       'create-user-page'));
       });
 
@@ skipping 25 matching lines @@
         createProfileElement = pagesElement.$$('create-profile');
         assertTrue(!createProfileElement);
       });
     });
   }
 
   return {
     registerTests: registerTests,
   };
 });