Add generic interfaces for the sinks of the media stream audio track

content/public/renderer/media_stream_audio_sink.cc

+// Copyright 2013 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 "content/public/renderer/media_stream_audio_sink.h"
+
+#include "base/logging.h"
+#include "content/renderer/media/media_stream_track_extra_data.h"
+#include "content/renderer/media/webrtc_local_audio_track.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamTrack.h"
+
+namespace content {
+
+void AddToAudioTrack(MediaStreamAudioSink* sink,
+                     const blink::WebMediaStreamTrack& track) {
+  DCHECK(track.source().type() == blink::WebMediaStreamSource::TypeAudio);
+  MediaStreamTrackExtraData* extra_data =

[Alpha Left Google, 2013/12/02 19:11:38]

track.isNull() can be true and extra_data can also be NULL. It should be checked
here and return a boolean.

[no longer working on chromium, 2013/12/03 11:45:45]

The sinks are depending on the track, and they should outlive the track by
holding a blink track object, which is a smart pointer. So the track and the
extra data should be always valid. If not, then it is considered to be
programming error and needs to be fixed.

I did some local tests and the current code works. In case the track goes away
before the sink, which is considered as programming error and will crash chrome.
Then we will know and fix the real problem.

+      static_cast<MediaStreamTrackExtraData*>(track.extraData());
+  DCHECK(extra_data->is_local_track());
+  WebRtcLocalAudioTrack* audio_track =
+      static_cast<WebRtcLocalAudioTrack*>(extra_data->track().get());
+  audio_track->AddSink(sink);
+}
+
+void RemoveFromAudioTrack(MediaStreamAudioSink* sink,
+                          const blink::WebMediaStreamTrack& track) {
+  MediaStreamTrackExtraData* extra_data =
+      static_cast<MediaStreamTrackExtraData*>(track.extraData());
+  DCHECK(extra_data->is_local_track());
+  WebRtcLocalAudioTrack* audio_track =
+      static_cast<WebRtcLocalAudioTrack*>(extra_data->track().get());
+  audio_track->RemoveSink(sink);
+}
+
+}  // namespace content