Have bindings layer assume and insist that all interface types are GCed.

third_party/WebKit/Source/core/dom/DOMStringList.idl

 /*
  * Copyright (C) 2010 Google Inc. All Rights Reserved.
  *
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  * modification, are permitted provided that the following conditions
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 // https://dom.spec.whatwg.org/#domstringlist
 
 // FIXME: DOMStringList has been removed from the spec. crbug.com/460726
 [
-    GarbageCollected,
 ] interface DOMStringList {
     readonly attribute unsigned long length;
     getter DOMString? (unsigned long index);
 
     [CallWith=ExecutionContext] DOMString? item(unsigned long index);
     [CallWith=ExecutionContext,MeasureAs=DOMStringListContains] boolean contains(DOMString string);
 };