Add support for [TreatNullAs] extended attribute for reflected attributes

Source/core/html/HTMLOutputElement.idl

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
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 interface HTMLOutputElement : HTMLElement {
     readonly attribute DOMSettableTokenList htmlFor;
     readonly attribute HTMLFormElement form;
-    [Reflect] attribute DOMString name;
+    [Reflect, TreatNullAs=NullString] attribute DOMString name;
 
     readonly attribute DOMString type;
     [TreatNullAs=NullString] attribute DOMString defaultValue;
     [TreatNullAs=NullString] attribute DOMString value;
 
     readonly attribute boolean willValidate;
     readonly attribute ValidityState validity;
     readonly attribute DOMString validationMessage;
     boolean checkValidity();
     void setCustomValidity([TreatNullAs=NullString, TreatUndefinedAs=NullString] DOMString error);
 
     readonly attribute NodeList labels;
 };