Add SourceBuffer implementations of Audio/VideoTracks

third_party/WebKit/Source/modules/mediasource/SourceBufferTrackBaseSupplement.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 SourceBufferTrackBaseSupplement_h
+#define SourceBufferTrackBaseSupplement_h
+
+#include "platform/Supplementable.h"
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+class TrackBase;
+class SourceBuffer;
+
+class SourceBufferTrackBaseSupplement : public GarbageCollected<SourceBufferTrackBaseSupplement>, public HeapSupplement<TrackBase> {
+    USING_GARBAGE_COLLECTED_MIXIN(SourceBufferTrackBaseSupplement);
+public:
+    explicit SourceBufferTrackBaseSupplement(TrackBase&, SourceBuffer*);

[philipj_slow, 2016/04/05 14:52:26]

Can you make this constructor private and have a static from(TrackBase&) that's
idempotent? Then instead of a bare new SourceBufferTrackBaseSupplement you'd
have a from(trackList).setSourceBuffer(...) or similar.

The current setup looks a bit fragile in that the constructor can be called
twice.

+
+    static SourceBuffer* sourceBuffer(TrackBase&);
+
+    DECLARE_VIRTUAL_TRACE();
+
+private:
+    Member<SourceBuffer> m_sourceBuffer;
+};
+
+} // namespace blink
+
+#endif
+