Add constructors to all the event classes.

client/html/src/MutationEventWrappingImplementation.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 MutationEventWrappingImplementation extends EventWrappingImplementation implements MutationEvent {
   MutationEventWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
 
+  factory MutationEventWrappingImplementation(String type, Node relatedNode,
+      String prevValue, String newValue, String attrName, int attrChange,
+      [bool canBubble = false, bool cancelable = false]) {
+    var e = dom.document.createEvent("MutationEvent");
+    e.initMutationEvent(type, canBubble, cancelable,
+        LevelDom.unwrap(relatedNode), prevValue, newValue, attrName,
+        attrChange);
+    return LevelDom.wrapMutationEvent(e);
+  }
+
   int get attrChange() { return _ptr.attrChange; }
 
   String get attrName() { return _ptr.attrName; }
 
   String get newValue() { return _ptr.newValue; }
 
   String get prevValue() { return _ptr.prevValue; }
 
   Node get relatedNode() { return LevelDom.wrapNode(_ptr.relatedNode); }
-
-  void initMutationEvent(String type, bool canBubble, bool cancelable, Node relatedNode, String prevValue, String newValue, String attrName, int attrChange) {
-    _ptr.initMutationEvent(type, canBubble, cancelable, LevelDom.unwrap(relatedNode), prevValue, newValue, attrName, attrChange);
-    return;
-  }
 }