Add constructors to all the event classes.

client/html/src/CustomEventWrappingImplementation.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 CustomEventWrappingImplementation extends EventWrappingImplementation implements CustomEvent {
+  CustomEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
 
-class CustomEventWrappingImplementation extends EventWrappingImplementation implements CustomEvent {
-  CustomEventWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
+  factory CustomEventWrappingImplementation(String type,
+      [bool canBubble = true, bool cancelable = true, Object detail = null]) {
+    final e = dom.document.createEvent("CustomEvent");
+    e.initCustomEvent(type, canBubble, cancelable, detail);
+    return LevelDom.wrapCustomEvent(e);
+  }
 
-  String get detail() { return _ptr.detail; }
-
-  void initCustomEvent(String typeArg, bool canBubbleArg, bool cancelableArg, Object detailArg) {
-    _ptr.initCustomEvent(typeArg, canBubbleArg, cancelableArg, LevelDom.unwrapMaybePrimitive(detailArg));
-    return;
-  }
+  String get detail() => _ptr.detail;
 }