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

third_party/WebKit/Source/modules/vr/VRFieldOfViewInit.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // http://mozvr.github.io/webvr-spec/webvr.html#vrfieldofview
 [
     RuntimeEnabled=WebVR,
-    GarbageCollected
 ] dictionary VRFieldOfViewInit {
     double upDegrees = 0.0;
     double rightDegrees = 0.0;
     double downDegrees = 0.0;
     double leftDegrees = 0.0;
 };