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

third_party/WebKit/Source/modules/remoteplayback/RemotePlayback.idl

 // Copyright 2016 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.
 
 // https://w3c.github.io/remote-playback/#idl-def-remoteplayback
 
 enum RemotePlaybackState {
     "connected",
     "disconnected"
 };
 
 [
-    GarbageCollected,
     RuntimeEnabled=RemotePlayback
 ] interface RemotePlayback : EventTarget {
     readonly attribute RemotePlaybackState state;
     attribute EventHandler onstatechange;
 
     [CallWith=ScriptState] Promise<RemotePlaybackAvailability> getAvailability();
     [CallWith=ScriptState] Promise<bool> connect();
 };