Support FormData on WorkerGlobalScope.

Source/core/html/FormData.idl

 /*
  * Copyright (C) 2010 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:
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  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 11 matching lines @@
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  * 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
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 [
+    Constructor([Default=Undefined] optional HTMLFormElement form),

[arv (Not doing code reviews), 2014/04/07 21:16:38]

Can we skip [Default=Undefined] and just declare a constructor with
`HTMLFormElement* form = 0` instead?

[sof, 2014/04/08 15:10:53]

Ought to, but non-default optional constructor args aren't handled correctly by
the code generator. Addressing.

[sof, 2014/04/08 19:36:50]

That's simpler, changed to do so. Also removed the passing of ExecutionContext
to the constructor, it wasn't serving an effective purpose.

+    ConstructorCallWith=ExecutionContext,
+    GlobalContext=Window&WorkerGlobalScope,
+    ImplementedAs=DOMFormData,
     WillBeGarbageCollected,
-    Constructor([Default=Undefined] optional HTMLFormElement form),
-    ImplementedAs=DOMFormData
 ] interface FormData {
     void append(DOMString name, Blob value, optional DOMString filename);
     void append(DOMString name, DOMString value);
 };