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

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

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  * Copyright (C) 2012 Motorola Mobility Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 13 matching lines @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://url.spec.whatwg.org/#url
 
 [
     Constructor(USVString url, optional USVString base),
     Exposed=(Window,Worker),
     ImplementedAs=DOMURL,
     RaisesException=Constructor,
-    GarbageCollected,
 ] interface URL {
     // TODO(philipj): Implement domainToASCII() and domainToUnicode().
     // crbug.com/493908
     // static USVString domainToASCII(USVString domain);
     // static USVString domainToUnicode(USVString domain);
 
     // TODO(philipj): This should be in a partial interface definition:
     // File API
     // https://w3c.github.io/FileAPI/#creating-revoking
     // TODO(philipj): The return type should not be nullable.
     [RaisesException, CallWith=ExecutionContext] static DOMString? createObjectURL(Blob blob);
     [CallWith=ExecutionContext] static void revokeObjectURL(DOMString url);
     readonly attribute URLSearchParams searchParams;
 };
 
 URL implements URLUtils;