Add constructors to all the event classes.

client/html/src/ErrorEvent.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.
+interface ErrorEvent extends Event factory ErrorEventWrappingImplementation {
 
-interface ErrorEvent extends Event {
+  ErrorEvent(String type, String message, String filename, int lineNo,
+      [bool canBubble, bool cancelable]);
 
   String get filename();
 
   int get lineno();
 
   String get message();
-
-  void initErrorEvent(String typeArg, bool canBubbleArg, bool cancelableArg, String messageArg, String filenameArg, int linenoArg);
 }