MD Settings: Deflake attempt for CrSettingsPrivacyPageTest.PrivacyPage.

chrome/test/data/webui/settings/privacy_page_test.js

Index: chrome/test/data/webui/settings/privacy_page_test.js
diff --git a/chrome/test/data/webui/settings/privacy_page_test.js b/chrome/test/data/webui/settings/privacy_page_test.js
index c42bbe0f9ba0a1f3d96285ec1cd70d4c7d0ddebd..f317e13c415e53ef5bcaef4dcc7c75887f84d27c 100644
--- a/chrome/test/data/webui/settings/privacy_page_test.js
+++ b/chrome/test/data/webui/settings/privacy_page_test.js
@@ -101,7 +101,17 @@ cr.define('settings_privacy_page', function() {
 
       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();