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

Source/modules/encoding/TextDecoder.idl

 /*
  * Copyright (C) 2013 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 12 matching lines @@
  * 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.
  */
 
 [
     RuntimeEnabled=EncodingAPI,
-    GlobalContext=Window&WorkerGlobalScope,
+    Exposed=Window&Worker,
     Constructor([Default=NullString] optional DOMString label, optional Dictionary options),
     RaisesException=Constructor,
     GarbageCollected
 ] interface TextDecoder {
     readonly attribute DOMString encoding;
     [RaisesException] DOMString decode(optional ArrayBufferView input, optional Dictionary options);
 };