Implement disabling and enabling media tracks

media/renderers/audio_renderer_impl.cc

Index: media/renderers/audio_renderer_impl.cc
diff --git a/media/renderers/audio_renderer_impl.cc b/media/renderers/audio_renderer_impl.cc
index a1cbd485783103ef4715d22428f605d0ba750964..d742ebc851d600394e4ede546d6270c4f9927596 100644
--- a/media/renderers/audio_renderer_impl.cc
+++ b/media/renderers/audio_renderer_impl.cc
@@ -291,6 +291,7 @@ void AudioRendererImpl::DoFlush_Locked() {
   DCHECK(!pending_read_);
   DCHECK_EQ(state_, kFlushed);
 
+  ended_timestamp_ = kInfiniteDuration();

[chcunningham, 2016/06/24 23:32:55]

This seems like the right thing - just curious how you found this wasn't being
done?

[servolk, 2016/06/25 00:36:33]

I've been testing this CL manually, trying a bunch of different things
(enable/disable a/v streams, seek/pause/resume while one of the streams is
disabled, etc), and noticed that audio stream playback would sometimes stall
when re-enabling and audio stream after it's been disabled and a seek to a
different position has occured. I've debugged that stall and noticed that we
need to reset |ended_timestamp_| during the Flush even if that Flush is not
followed by SetMediaTime, since when we are restarting the audio stream, we do a
flush, but we don't do an explicit SetMediaTime.

   audio_buffer_stream_->Reset(base::Bind(&AudioRendererImpl::ResetDecoderDone,
                                          weak_factory_.GetWeakPtr()));
 }