Adding a test for UListElement

tests/html/element_types_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library element_types;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 main() {
@@ skipping 268 matching lines @@
       expect((new Element.tag('tbody')) is TableSectionElement, true);
       expect((new Element.tag('tfoot')) is TableSectionElement, true);
       expect((new Element.tag('thead')) is TableSectionElement, true);
     });
     test('track', () {
       expect((new Element.tag('track')) is TrackElement,
           TrackElement.supported);
     });
     test('ul', () {
       expect((new UListElement()) is UListElement, true);
+      var ul = new UListElement();
+      var li = new LIElement();
+      ul.append(li);
     });
     test('video', () {
       expect((new VideoElement()) is VideoElement, true);
     });
     test('unknown', () {
       expect((new Element.tag('someunknown')) is UnknownElement, true);
     });;
   });
 }