MD Settings: Defer opening Import Dialog dialog to prevent UI flicker

chrome/test/data/webui/settings/import_data_dialog_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.
 
 /**
  * @constructor
  * @implements {settings.ImportDataBrowserProxy}
  * @extends {settings.TestBrowserProxy}
  */
 var TestImportDataBrowserProxy = function() {
@@ skipping 77 matching lines @@
   var dialog = null;
 
   setup(function() {
     browserProxy = new TestImportDataBrowserProxy();
     browserProxy.setBrowserProfiles(browserProfiles);
     settings.ImportDataBrowserProxyImpl.instance_ = browserProxy;
     PolymerTest.clearBody();
     dialog = document.createElement('settings-import-data-dialog');
     dialog.set('prefs', prefs);
     document.body.appendChild(dialog);
-    assertTrue(dialog.$.dialog.open);
     return browserProxy.whenCalled('initializeImportDialog').then(function() {
+      assertTrue(dialog.$.dialog.open);
       Polymer.dom.flush();
     });
   });
 
   function simulateBrowserProfileChange(index) {
     dialog.$.browserSelect.selectedIndex = index;
     dialog.$.browserSelect.dispatchEvent(new CustomEvent('change'));
   }
 
   test('Initialization', function() {
@@ skipping 82 matching lines @@
       assertFalse(dialog.$.successIcon.parentElement.hidden);
       assertTrue(dialog.$$('settings-toggle-button').parentElement.hidden);
     });
   });
 
   test('ImportError', function() {
     simulateImportStatusChange(settings.ImportDataStatus.FAILED);
     assertFalse(dialog.$.dialog.open);
   });
 });