IDL: Further improve indexed/named property setter type checking

Source/bindings/tests/idls/core/TestInterface2.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 28 matching lines @@
     SetWrapperReferenceFrom=ownerNode, // Conflicts with [SetWrapperReferenceTo]
     // Note that Exposed(Arguments) has no effect on bindings-tests. It is
     // processed in generate_global_constructors.py.
     Exposed(Window FeatureName), // Conflicts with Exposed=(Window,Worker)
 ] interface TestInterface2 {
     // This interface has only runtime enabled constants.
     [RuntimeEnabled=FeatureName] const unsigned short CONST_VALUE_1 = 1;
 
     // Indexed property operations with an identifier
     [RaisesException] getter TestInterfaceEmpty item(unsigned long index);
-    [RaisesException] setter DOMString setItem(unsigned long index, DOMString value);
+    [RaisesException, TypeChecking=Interface] setter TestInterfaceEmpty setItem(unsigned long index, TestInterfaceEmpty value);
     [RaisesException] deleter boolean deleteItem(unsigned long index);
 
     // Named property operations with an identifier
     [RaisesException] getter TestInterfaceEmpty namedItem(DOMString name);
-    [RaisesException] setter DOMString setNamedItem(DOMString name, DOMString value);
+    [RaisesException, TypeChecking=Interface] setter TestInterfaceEmpty setNamedItem(DOMString name, TestInterfaceEmpty? value);
     [RaisesException] deleter boolean deleteNamedItem(DOMString name);
 
     stringifier DOMString stringifierMethod();
 
     readonly setlike<TestInterfaceEmpty>;
 };