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 83 matching lines @@
       /** @type {SettingsPrivacyPageElement} */
       var page;
 
       setup(function() {
         page = document.createElement('settings-privacy-page');
         document.body.appendChild(page);
       });
 
       teardown(function() { page.remove(); });
 
-      test('showClearBrowsingDataDialog', function() {
+      test('showClearBrowsingDataDialog', function(done) {
+        // Ensure that the dialog is fully opened before returning from this
+        // test, otherwise asynchronous code run in attached() can cause flaky
+        // errors.
+        page.addEventListener(
+            'clear-browsing-data-dialog-opened', function() {

[Dan Beam, 2016/09/14 01:15:58]

can we just use 'show' instead of making this event?

[dpapad, 2016/09/15 16:56:17]

Do you mean use show() instead of showModal() to display the dialog? If so, no
can't do that (non-modal dialogs look and behave differently).

We could avoid the event though, by using a MutationObserver for the dialog's
'open' attribute. We already do that at
https://cs.chromium.org/chromium/src/chrome/test/data/webui/settings/certific....
If you prefer that, perhaps we could reuse the MutationObserver code, instead of
repeating across files.

[Dan Beam, 2016/09/15 17:11:06]

i thought, for some reason, that a 'show' event was dispatched.  dang, guess
not.
that would make sense.  it /might/ even make sense to add a onAttributeChange()
generic method to util.js, as michaelpg@ just did with: listenOnce
https://cs.chromium.org/chromium/src/ui/webui/resources/js/util.js?q=util.js&...

or we could just add a show() method override in CrDialogElement and call
this.fire('show').

[dpapad, 2016/09/15 17:58:22]

I followed similar approach, but I did not add it in util.js, since it is only
needed by tests. I created a test_util.js file (similar to
chrome/test/data/webui/md_history/test_util.js), and I moved there the new
shared method, as well as addressed a TODO to stop duplicating the
eventToPromise() helper method.

+              assertTrue(page.$$(
+                  'settings-clear-browsing-data-dialog').$.dialog.open);
+              done();
+            });
+
         assertFalse(!!page.$$('settings-clear-browsing-data-dialog'));
         MockInteractions.tap(page.$.clearBrowsingData);
         Polymer.dom.flush();
         assertTrue(!!page.$$('settings-clear-browsing-data-dialog'));
       });
     });
   }
 
   function registerClearBrowsingDataTests() {
     suite('ClearBrowsingData', function() {
@@ skipping 137 matching lines @@
   return {
     registerTests: function() {
       if (cr.isMac || cr.isWin)
         registerNativeCertificateManagerTests();
 
       registerClearBrowsingDataTests();
       registerPrivacyPageTests();
     },
   };
 });