Support optional, non-defaulted constructor arguments.

Source/bindings/tests/idls/TestInterfaceConstructor2.idl

Index: Source/bindings/tests/idls/TestInterfaceConstructor2.idl
diff --git a/Source/bindings/tests/idls/TestInterfaceConstructor2.idl b/Source/bindings/tests/idls/TestInterfaceConstructor2.idl
index d42461e8dfa83edb872f057d7a3455b60a92ce4a..b9d045cfc3f36c3b842be83d93731cd72d734677 100644
--- a/Source/bindings/tests/idls/TestInterfaceConstructor2.idl
+++ b/Source/bindings/tests/idls/TestInterfaceConstructor2.idl
@@ -43,6 +43,7 @@
         long longArg,
         [Default=Undefined] optional DOMString defaultUndefinedOptionalStringArg,
         [Default=NullString] optional DOMString defaultNullStringOptionalStringArg,
-        [Default=Undefined] optional Dictionary defaultUndefinedOptionalDictionaryArg),
+        [Default=Undefined] optional Dictionary defaultUndefinedOptionalDictionaryArg,
+        optional DOMString optionalStringArg),
 ] interface TestInterfaceConstructor2 {
 };