Support optional, non-defaulted constructor arguments.

Source/bindings/tests/idls/TestInterfaceConstructor2.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:
  *
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@@ skipping 24 matching lines @@
 //
 // Also includes some [Default] arguments (instead of in
 // TestInterfaceConstructor.idl), otherwise overload resolution check string is
 // extremely long and triggers a lint warning (line length).
 [
     Constructor(DOMString stringArg),
     Constructor(
         TestInterfaceEmpty testInterfaceEmptyArg,
         long longArg,
         [Default=Undefined] optional DOMString defaultUndefinedOptionalStringArg,
-        [Default=NullString] optional DOMString defaultNullStringOptionalStringArg,
-        [Default=Undefined] optional Dictionary defaultUndefinedOptionalDictionaryArg),
+        [Default=Undefined] optional Dictionary defaultUndefinedOptionalDictionaryArg,

[Nils Barth (inactive), 2014/04/10 01:01:23]

? Could you keep the [Default=NullString] argument ?

[sof, 2014/04/10 06:16:40]

Done.

+        optional DOMString optionalStringArg),
 ] interface TestInterfaceConstructor2 {
 };