Implement AudioTrack, AudioTrackList, VideoTrack, and VideoTrackList

Source/core/html/track/AudioTrackList.idl

Index: Source/core/html/track/AudioTrackList.idl
diff --git a/Source/core/html/track/AudioTrackList.idl b/Source/core/html/track/AudioTrackList.idl
new file mode 100644
index 0000000000000000000000000000000000000000..caf4046ad8e494f35bb85abe98793134457edd56
--- /dev/null
+++ b/Source/core/html/track/AudioTrackList.idl
@@ -0,0 +1,15 @@
+// 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.
+
+[
+    RuntimeEnabled=AudioVideoTracks,
+] 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;
+};