Allow media track switching.

media/renderers/renderer_impl.h

Index: media/renderers/renderer_impl.h
diff --git a/media/renderers/renderer_impl.h b/media/renderers/renderer_impl.h
index f55a7635e22707644c5b818813542d23a49544c0..4206a90311498c1e2b43e31967589264c1d3d3f9 100644
--- a/media/renderers/renderer_impl.h
+++ b/media/renderers/renderer_impl.h
@@ -106,8 +106,29 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
   void FlushVideoRenderer();
   void OnVideoRendererFlushDone();
 
-  void RestartAudioRenderer(base::TimeDelta time);
-  void RestartVideoRenderer(base::TimeDelta time);
+  // Reinitialize audio/video renderer during a media track switching. The
+  // renderer must be flushed first, and when the re-init is completed the
+  // corresponding callback will be invoked to restart playback.
+  // The |stream| parameter specifies the demuxer stream representing the new
+  // media track. And the |time| parameter specifies the time on media timeline
+  // where the switch occured.

[xhwang, 2017/03/29 00:16:47]

nit: At this level, we are dealing with DemuxerStream swiching (StatusChange)
and we don't need to mention "media track". People looking at this code would
have no idea what a media track is.

[servolk, 2017/03/29 01:49:33]

Done.

+  void ReinitializeAudioRenderer(DemuxerStream* stream, base::TimeDelta time);
+  void OnAudioRendererReinitialized(DemuxerStream* stream,
+                                    base::TimeDelta time,
+                                    PipelineStatus status);
+  void ReinitializeVideoRenderer(DemuxerStream* stream, base::TimeDelta time);
+  void OnVideoRendererReinitialized(DemuxerStream* stream,
+                                    base::TimeDelta time,
+                                    PipelineStatus status);
+
+  // Restart audio/video renderer playback after a media track switch or after a
+  // media track has been disabled and re-enabled. The |stream| parameter

[xhwang, 2017/03/29 00:16:47]

ditto about "media track"

[servolk, 2017/03/29 01:49:33]

Done.

+  // specifies which stream needs to be restarted. The |time| parameter
+  // specifies the position on the media timeline where the playback needs to be
+  // restarted. It is necessary for demuxers with independent streams (e.g. MSE
+  // / ChunkDemuxer) to synchronize data reading between those streams.
+  void RestartAudioRenderer(DemuxerStream* stream, base::TimeDelta time);
+  void RestartVideoRenderer(DemuxerStream* stream, base::TimeDelta time);
 
   // Callback executed by filters to update statistics.
   void OnStatisticsUpdate(const PipelineStatistics& stats);
@@ -166,6 +187,9 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
   std::unique_ptr<AudioRenderer> audio_renderer_;
   std::unique_ptr<VideoRenderer> video_renderer_;
 
+  DemuxerStream* current_audio_stream_;
+  DemuxerStream* current_video_stream_;
+
   // Renderer-provided time source used to control playback.
   TimeSource* time_source_;
   std::unique_ptr<WallClockTimeSource> wall_clock_time_source_;