Roll 50: Copied IDLs, PYTHON scripts from WebKit removed deleted files in WebCore

core/html/track/AudioTrackList.idl

 // Copyright 2014 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://html.spec.whatwg.org/#audiotracklist
 
 [
+    GarbageCollected,
     RuntimeEnabled=AudioVideoTracks,
     SetWrapperReferenceFrom=owner,
 ] interface AudioTrackList : EventTarget {
   readonly attribute unsigned long length;
   getter AudioTrack (unsigned long index);
   AudioTrack? getTrackById(DOMString id);
 
   attribute EventHandler onchange;
   attribute EventHandler onaddtrack;
   attribute EventHandler onremovetrack;
 };