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

third_party/WebKit/Source/core/clipboard/DataTransferItemList.idl

 /*
  * Copyright (C) 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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://html.spec.whatwg.org/#the-datatransferitemlist-interface
 
 [
-    GarbageCollected,
 ] interface DataTransferItemList {
     readonly attribute unsigned long length;
     [ImplementedAs=item] getter DataTransferItem (unsigned long index);
     [RaisesException] DataTransferItem? add(DOMString data, DOMString type);
     // TODO(philipj): The file argument should not be nullable.
     DataTransferItem? add(File? file);
     [RaisesException, ImplementedAs=deleteItem] void remove(unsigned long index);
     void clear();
 };