MD Settings: Deflake attempt for CrSettingsPrivacyPageTest.PrivacyPage.

chrome/test/data/webui/settings/privacy_page_test.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('settings_privacy_page', function() {
   /**
    * @constructor
    * @extends {TestBrowserProxy}
    * @implements {settings.PrivacyPageBrowserProxy}
    */
@@ skipping 87 matching lines @@
         page = document.createElement('settings-privacy-page');
         document.body.appendChild(page);
       });
 
       teardown(function() { page.remove(); });
 
       test('showClearBrowsingDataDialog', function() {
         assertFalse(!!page.$$('settings-clear-browsing-data-dialog'));
         MockInteractions.tap(page.$.clearBrowsingData);
         Polymer.dom.flush();
-        assertTrue(!!page.$$('settings-clear-browsing-data-dialog'));
+
+        var dialog = page.$$('settings-clear-browsing-data-dialog');
+        assertTrue(!!dialog);
+
+        // Ensure that the dialog is fully opened before returning from this
+        // test, otherwise asynchronous code run in attached() can cause flaky
+        // errors.
+        return dialog.$.dialog.open ?
+            Promise.resolve() :
+            test_util.whenAttributeChanges(dialog.$.dialog, 'open');
       });
     });
   }
 
   function registerClearBrowsingDataTests() {
     suite('ClearBrowsingData', function() {
       /** @type {settings.TestClearBrowsingDataBrowserProxy} */
       var testBrowserProxy;
 
       /** @type {SettingsClearBrowsingDataDialogElement} */
@@ skipping 133 matching lines @@
   return {
     registerTests: function() {
       if (cr.isMac || cr.isWin)
         registerNativeCertificateManagerTests();
 
       registerClearBrowsingDataTests();
       registerPrivacyPageTests();
     },
   };
 });