Reverting setTimeout removal.

tests/html/transition_event_test.dart

 // Copyright (c) 2013, 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 transition_event_test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
-import 'dart:async';
 
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported', () {
     test('supported', () {
       expect(CssStyleDeclaration.supportsTransitions, true);
     });
   });
 
   group('functional', () {
     test('transitionEnd', () {
       if (CssStyleDeclaration.supportsTransitions) {
         var element = new DivElement();
         document.body.append(element);
 
         element.style.opacity = '0';
         element.style.width = '100px';
         element.style.height = '100px';
         element.style.background = 'red';
         element.style.transition = 'opacity .1s';
 
-        new Timer(const Duration(milliseconds: 100), expectAsync0(() {
+        window.setTimeout(expectAsync0(() {
           element.onTransitionEnd.first.then(expectAsync1((e) {
             expect(e is TransitionEvent, isTrue);
             expect(e.propertyName, 'opacity');
           }));
 
           element.style.opacity = '1';
-        }));
+        }), 100);
       }
     });
   });
 }