Add constructors to all the event classes.

client/html/src/ProgressEvent.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 ProgressEvent extends Event factory ProgressEventWrappingImplementation {
 
-interface ProgressEvent extends Event {
+  ProgressEvent(String type, int loaded, [bool canBubble, bool cancelable,
+      bool lengthComputable, int total]);
 
   bool get lengthComputable();
 
   int get loaded();
 
   int get total();
-
-  void initProgressEvent(String typeArg, bool canBubbleArg, bool cancelableArg, bool lengthComputableArg, int loadedArg, int totalArg);
 }