Add constructors to all the event classes.

client/html/src/MessageEventWrappingImplementation.dart

 // Copyright (c) 2011, 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.
 
-// WARNING: Do not edit - generated code.
+class MessageEventWrappingImplementation extends EventWrappingImplementation implements MessageEvent {
+  MessageEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
 
-class MessageEventWrappingImplementation extends EventWrappingImplementation implements MessageEvent {
-  MessageEventWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
+  factory MessageEventWrappingImplementation(String type, String data,
+      String origin, String lastEventId, Window source, MessagePort port,
+      [bool canBubble = true, bool cancelable = true]) {
+    final e = dom.document.createEvent("MessageEvent");
+    e.initMessageEvent(type, canBubble, cancelable, data, origin, lastEventId,
+        LevelDom.unwrap(source), LevelDom.unwrap(port));
+    return LevelDom.wrapMessageEvent(e);
+  }
 
-  String get data() { return _ptr.data; }
+  String get data() => _ptr.data;
 
-  String get lastEventId() { return _ptr.lastEventId; }
+  String get lastEventId() => _ptr.lastEventId;
 
-  MessagePort get messagePort() { return LevelDom.wrapMessagePort(_ptr.messagePort); }
+  MessagePort get messagePort() => LevelDom.wrapMessagePort(_ptr.messagePort);
 
-  String get origin() { return _ptr.origin; }
+  String get origin() => _ptr.origin;
 
-  Window get source() { return LevelDom.wrapWindow(_ptr.source); }
+  Window get source() => LevelDom.wrapWindow(_ptr.source);
 
   void initMessageEvent(String typeArg, bool canBubbleArg, bool cancelableArg, String dataArg, String originArg, String lastEventIdArg, Window sourceArg, MessagePort messagePort) {
     _ptr.initMessageEvent(typeArg, canBubbleArg, cancelableArg, dataArg, originArg, lastEventIdArg, LevelDom.unwrap(sourceArg), LevelDom.unwrap(messagePort));
     return;
   }
 }