Adding constructor to ContentElement.

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('TransferableTest');
+#library('contentelement_test');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   useHtmlConfiguration();
 
-  test('TransferableTest', () {
-    window.on.message.add(expectAsync1((messageEvent) {
-      expect(messageEvent.data, new isInstanceOf<ArrayBuffer>());
-    }));
-    final buffer = (new Float32Array(3)).buffer;
-    window.webkitPostMessage(buffer, '*', [buffer]);
-  });
+  test('constructor', () {
+      var e = new ContentElement();
+      Expect.isTrue(e is ContentElement);
+    });
 }