Add SourceBuffer implementations of Audio/VideoTracks

third_party/WebKit/Source/modules/mediasource/AudioTrackSourceBuffer.idl

Index: third_party/WebKit/Source/modules/mediasource/AudioTrackSourceBuffer.idl
diff --git a/third_party/WebKit/Source/modules/mediasource/AudioTrackSourceBuffer.idl b/third_party/WebKit/Source/modules/mediasource/AudioTrackSourceBuffer.idl
new file mode 100644
index 0000000000000000000000000000000000000000..35f26b94bcd89aef8069c6d3aaa60962cae48c53
--- /dev/null
+++ b/third_party/WebKit/Source/modules/mediasource/AudioTrackSourceBuffer.idl
@@ -0,0 +1,12 @@
+// 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/media-source/#audio-track-extensions
+[
+    GarbageCollected,
+    ImplementedAs=SourceBufferTrackBaseSupplement,

[philipj_slow, 2016/04/05 14:56:11]

If you make the other suggested change, I think you could also consider dropping
this, and instead just having AudioTrackSourceBuffer.h with a single static
method that does return from(someContext).sourceBuffer() instead.

+    RuntimeEnabled=AudioVideoTracks
+] partial interface AudioTrack {
+    readonly attribute SourceBuffer? sourceBuffer;
+};