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..a5610d8143581bda300541b2852ffc93e712bbcd 100644
--- a/chrome/test/data/webui/settings/privacy_page_test.js
+++ b/chrome/test/data/webui/settings/privacy_page_test.js
@@ -105,7 +105,16 @@ cr.define('settings_privacy_page', 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');
       });
     });
   }