Use Dart_InstanceIsSubtypeOf to check if instance is a direct subtype of specified type.

Source/bindings/dart/custom/DartHTMLOptionsCollectionCustom.cpp

 // Copyright 2011, 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 40 matching lines @@
 
         // Note: as of now HTMLSelect element doesn't implement List and therefore I inline v8's
         // toOptionsCollectionSetter right here. If situation changes later, this piece of code should
         // be refactored into helper method.
         unsigned index = DartUtilities::dartToUnsigned(Dart_GetNativeArgument(args, 1), exception);
         if (exception)
             goto fail;
 
         Dart_Handle elementArgument = Dart_GetNativeArgument(args, 2);
         DartDOMData* domData = static_cast<DartDOMData*>(Dart_GetNativeIsolateData(args));
-        if (!DartDOMWrapper::instanceOf<DartHTMLOptionElement>(domData, elementArgument)) {
+        if (!DartDOMWrapper::subtypeOf<DartHTMLOptionElement>(domData, elementArgument)) {
             exception = DartDOMWrapper::exceptionCodeToDartException(TypeMismatchError);
             goto fail;
         }
         HTMLOptionElement* element = DartHTMLOptionElement::toNative(elementArgument, exception);
         if (exception)
             goto fail;
 
         DartExceptionState es;
         base->setOption(index, element, es);
         if (es.hadException()) {
             exception = DartDOMWrapper::exceptionCodeToDartException(es);
             goto fail;
         }
 
         return;
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 }
 
 }