Add SourceBuffer implementations of Audio/VideoTracks

third_party/WebKit/Source/modules/mediasource/SourceBufferTrackBaseSupplement.cpp

+// 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.
+
+#include "modules/mediasource/SourceBufferTrackBaseSupplement.h"
+
+#include "core/html/track/TrackBase.h"
+#include "modules/mediasource/SourceBuffer.h"
+
+namespace blink {
+
+static const char* SupplementName = "SourceBufferTrackBaseSupplement";
+
+SourceBufferTrackBaseSupplement::SourceBufferTrackBaseSupplement(TrackBase& trackBase)
+{
+    provideTo(trackBase, SupplementName, this);
+}
+
+// static
+SourceBufferTrackBaseSupplement& SourceBufferTrackBaseSupplement::from(TrackBase& track)
+{
+    SourceBufferTrackBaseSupplement* supplement = static_cast<SourceBufferTrackBaseSupplement*>(Supplement<TrackBase>::from(track, SupplementName));
+    if (!supplement) {
+        supplement = new SourceBufferTrackBaseSupplement(track);
+    }
+    return *supplement;
+}
+
+// static
+SourceBuffer* SourceBufferTrackBaseSupplement::sourceBuffer(TrackBase& track)
+{
+    // We could use SourceBufferTrackBaseSupplement::from(track).m_sourceBuffer here, but the 'from' method always creates a new supplement if an
+    // existing one is not found, so using 'from' here would result in supplement being created even for tracks that never have non-null .sourceBuffer
+    // property (i.e. tracks created by HTMLMediaElement and not SourceBuffer).
+    SourceBufferTrackBaseSupplement* supplement = static_cast<SourceBufferTrackBaseSupplement*>(Supplement<TrackBase>::from(track, SupplementName));

[philipj_slow, 2016/04/07 08:59:35]

You're only doing this in one place, but CSSSelectorWatch and Fullscreen have
fromIfExists, which can then also be used in the implementation of from. Makes
it obvious what's going on even without a comment.

[servolk, 2016/04/07 17:03:55]

Ah, ok, thanks for pointing that out. If just wasn't aware about this. But if we
already have those other fromIfExists precedents, we can use the same pattern
here for consistency.

+    if (supplement)
+        return supplement->m_sourceBuffer;
+    return nullptr;
+}
+
+void SourceBufferTrackBaseSupplement::setSourceBuffer(SourceBuffer* sourceBuffer)
+{
+    m_sourceBuffer = sourceBuffer;
+}
+
+DEFINE_TRACE(SourceBufferTrackBaseSupplement)
+{
+    visitor->trace(m_sourceBuffer);
+    Supplement<TrackBase>::trace(visitor);
+}
+
+} // namespace blink
+