Add constructors to all the event classes.

client/html/src/MutationEvent.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 MutationEvent extends Event factory MutationEventWrappingImplementation {
 
-interface MutationEvent extends Event {
+  MutationEvent(String type, Node relatedNode, String prevValue,
+      String newValue, String attrName, int attrChange, [bool canBubble,
+      bool cancelable]);
 
   static final int ADDITION = 2;
 
   static final int MODIFICATION = 1;
 
   static final int REMOVAL = 3;
 
   int get attrChange();
 
   String get attrName();
 
   String get newValue();
 
   String get prevValue();
 
   Node get relatedNode();
-
-  void initMutationEvent(String type, bool canBubble, bool cancelable, Node relatedNode, String prevValue, String newValue, String attrName, int attrChange);
 }