Add initial support for [Exposed=xx] extended IDL attribute

Source/core/events/MessageEvent.idl

 /*
  * Copyright (C) 2007 Henry Mason <hmason@mac.com>
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 
 [
     EventConstructor,
-    GlobalContext=Window&WorkerGlobalScope,
+    Exposed=Window&Worker,
     RaisesException=Constructor,
     Custom=Wrap,
 ] interface MessageEvent : Event {
     [InitializedByEventConstructor] readonly attribute DOMString origin;
     [InitializedByEventConstructor] readonly attribute DOMString lastEventId;
     [InitializedByEventConstructor] readonly attribute EventTarget? source; // May be a Window or a MessagePort
     [InitializedByEventConstructor, Custom=Getter] readonly attribute any data;
     [InitializedByEventConstructor] readonly attribute MessagePort[] ports;
     [Custom, MeasureAs=InitMessageEvent] void initMessageEvent([Default=Undefined] optional DOMString typeArg,
                                    [Default=Undefined] optional boolean canBubbleArg,
                                    [Default=Undefined] optional boolean cancelableArg,
                                    [Default=Undefined] optional any dataArg,
                                    [Default=Undefined] optional DOMString originArg,
                                    [Default=Undefined] optional DOMString lastEventIdArg,
                                    [Default=Undefined] optional Window sourceArg,
                                    [Default=Undefined] optional MessagePort[] messagePorts);
 
     [Custom, MeasureAs=PrefixedInitMessageEvent] void webkitInitMessageEvent([Default=Undefined] optional DOMString typeArg,
                                          [Default=Undefined] optional boolean canBubbleArg,
                                          [Default=Undefined] optional boolean cancelableArg,
                                          [Default=Undefined] optional any dataArg,
                                          [Default=Undefined] optional DOMString originArg,
                                          [Default=Undefined] optional DOMString lastEventIdArg,
                                          [Default=Undefined] optional Window sourceArg,
                                          [Default=Undefined] optional MessagePort[] transferables);
 };