Missed a change in the rename from initCustomEvent -> $dom_initCustomEvent.

lib/html/src/shared_FactoryProviders.dart

 // Copyright (c) 2012, 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.
 
+class _CustomEventFactoryProvider {
+  static CustomEvent createCustomEvent(String type, [bool canBubble = true,
+      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]) {
     final _EventImpl e = _document.$dom_createEvent("Event");
     e.$dom_initEvent(type, canBubble, cancelable);
     return e;
   }
 }
 
 class _MouseEventFactoryProvider {
@@ skipping 83 matching lines @@
 }
 
 class _SVGSVGElementFactoryProvider {
   static SVGSVGElement createSVGSVGElement() {
     final el = new SVGElement.tag("svg");
     // The SVG spec requires the version attribute to match the spec version
     el.attributes['version'] = "1.1";
     return el;
   }
 }