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

third_party/WebKit/Source/core/frame/Navigator.idl

 /*
     Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
 
     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Library General Public License for more details.
 
     You should have received a copy of the GNU Library General Public License
     along with this library; see the file COPYING.LIB.  If not, write to
     the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     Boston, MA 02110-1301, USA.
 */
 
 // https://html.spec.whatwg.org/#the-navigator-object
 
 [
-    GarbageCollected,
 ] interface Navigator {
     // objects implementing this interface also implement the interfaces given below
 
     // TODO(philipj): vendorSub should be on NavigatorID.
     [MeasureAs=NavigatorVendorSub] readonly attribute DOMString vendorSub;
 
     // TODO(philipj): productSub and vendor are not yet in the spec:
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=27954
     [MeasureAs=NavigatorProductSub] readonly attribute DOMString productSub;
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=27786
     [MeasureAs=NavigatorVendor] readonly attribute DOMString vendor;
 };
 
 Navigator implements NavigatorCPU;
 Navigator implements NavigatorID;
 Navigator implements NavigatorLanguage;
 Navigator implements NavigatorOnLine;
 Navigator implements NavigatorStorageUtils;