Add constructor for CustomEvent.

lib/html/src/shared_FactoryProviders.dart

Index: lib/html/src/shared_FactoryProviders.dart
===================================================================
--- lib/html/src/shared_FactoryProviders.dart	(revision 13097)
+++ lib/html/src/shared_FactoryProviders.dart	(working copy)
@@ -2,6 +2,15 @@
 // 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.
 
+class _CustomEventFactoryProvider {
+  static CustomEvent createCustomEvent(String type, [bool canBubble = true,

[blois, 2012/10/02 17:14:06]

Nit- there isn't really any reason to have default properties here since the
defaults are being specified by the constructor and it's just passing through.

+      bool cancelable = true, Object detail = null]) {
+    final _CustomEventImpl e = _document.$dom_createEvent("CustomEvent");
+    e.$dom_initCustomEvent(type, canBubble, cancelable, detail);
+    return e;
+  }
+}
+
 class _EventFactoryProvider {
   static Event createEvent(String type, [bool canBubble = true,
       bool cancelable = true]) {