Add 'error' parameter to 'window.onerror' handlers.

Source/core/dom/ErrorEvent.idl

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 [
     ConstructorTemplate=Event
 ] interface ErrorEvent : Event {
     [InitializedByEventConstructor] readonly attribute DOMString message;
     [InitializedByEventConstructor] readonly attribute DOMString filename;
     [InitializedByEventConstructor] readonly attribute unsigned long lineno;
 
+    [InitializedByEventConstructor] readonly attribute any error;
+
     // FIXME: Part of the specification but not exposed yet.
     // No other browser seems to support it (except IE10 as 'colno').
     // [InitializedByEventConstructor] readonly attribute unsigned long column;
 };