Cleaning up event constructors

tests/html/serialized_script_value_test.dart

 library SerializedScriptValueTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'utils.dart';
 
 serializationTest(name, value) => test(name, () {
       // To check how value is serialized and deserialized, we create a MessageEvent.
-    final event = document.$dom_createEvent('MessageEvent');
-    event.initMessageEvent('', false, false, value, '', '', window, []);
+    final event = new MessageEvent('', data:value);
     verifyGraph(value, event.data);
 });
 
 
 main() {
   useHtmlConfiguration();
 
   serializationTest('null', null);
   serializationTest('int', 1);
   serializationTest('double', 2.39);
   serializationTest('string', 'hey!');
 
   final simpleMap = {'a': 100, 'b': 's'};
   final dagMap = { 'x': simpleMap, 'y': simpleMap };
   final cyclicMap = { 'b': dagMap };
   cyclicMap['a'] = cyclicMap;
   serializationTest('simple map', simpleMap);
   serializationTest('dag map', dagMap);
   serializationTest('cyclic map', cyclicMap);
 
   final simpleList = [ 100, 's'];
   final dagList = [ simpleList, simpleList ];
   final cyclicList = [ dagList ];
   cyclicList.add(cyclicList);
   serializationTest('simple list', simpleList);
   serializationTest('dag list', dagList);
   serializationTest('cyclic list', cyclicList);
 }