Modified unittest to use new argument syntax.

tests/html/contentelement_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('contentelement_test');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
   test('constructor', () {
       var e = new ContentElement();
-      expect(e is ContentElement);
+      expect(e, new isInstanceOf<ContentElement>('ContentElement'));
     });
 }