Support FormData on WorkerGlobalScope.

Source/core/html/FormData.idl

Index: Source/core/html/FormData.idl
diff --git a/Source/core/html/FormData.idl b/Source/core/html/FormData.idl
index fe146ce0708ae51b699c131ff1c3ac7667244fce..3d884d4535144bcfb8a14e740f1c8298de9f5f00 100644
--- a/Source/core/html/FormData.idl
+++ b/Source/core/html/FormData.idl
@@ -29,9 +29,11 @@
  */
 
 [
-    WillBeGarbageCollected,
     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.

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