Add SourceBuffer implementations of Audio/VideoTracks

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

+// 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.
+
+#ifndef AudioTrackSourceBuffer_h
+#define AudioTrackSourceBuffer_h
+
+#include "platform/Supplementable.h"
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+class AudioTrack;
+class SourceBuffer;
+
+class AudioTrackSourceBuffer final : public GarbageCollectedFinalized<AudioTrackSourceBuffer>, public HeapSupplement<AudioTrack> {

[philipj_slow, 2016/02/26 13:36:54]

Did you check if it's possible to have only a single HeapSupplement<TrackBase>?
Nothing is both an AudioTrack and a VideoTrack, so it ought to work? It could be
that you'll need to have almost-empty AudioTrackSourceBuffer and
VideoTrackSourceBuffer that merely forward to that shared implementation.

[servolk, 2016/02/27 01:03:45]

Good idea, I haven't tried that yet, I'll give it a try.

[servolk, 2016/03/03 03:39:26]

Done.

+    USING_GARBAGE_COLLECTED_MIXIN(AudioTrackSourceBuffer);
+public:
+    static AudioTrackSourceBuffer& from(AudioTrack&);
+    virtual ~AudioTrackSourceBuffer();
+
+    static SourceBuffer* sourceBuffer(AudioTrack&);
+
+    DECLARE_VIRTUAL_TRACE();
+
+private:
+    static const char* supplementName();
+    explicit AudioTrackSourceBuffer(SourceBuffer*);
+
+    WeakMember<SourceBuffer> m_sourceBuffer;

[philipj_slow, 2016/02/26 13:36:54]

Should this really be weak? If a script has a reference to an AudioTrack but has
never looked at the sourceBuffer attribute (so it doesn't have a wrapper or
another reference), the SourceBuffer should still be kept alive for as long as
its possible that the script will peek at the sourceBuffer attribute. In other
words, Member<SourceBuffer>?

[servolk, 2016/02/27 01:03:45]

I don't know much about oilpan/GC being used by blink, so I was worried that if
the GC is using refcounting then using a strong Member reference here would
create a loop (since SourceBuffer already had strong refs to its tracks). Can
oilpan handle reference loops?

[fs, 2016/02/29 11:11:11]

Oilpan handles reference-loops (it is one of the higher-ranking reasons to have
it I'd say.)

[servolk, 2016/03/03 03:39:26]

Done.

+};
+
+} // namespace blink
+
+#endif