Implement disabling and enabling media tracks

media/base/pipeline.h

Index: media/base/pipeline.h
diff --git a/media/base/pipeline.h b/media/base/pipeline.h
index 0a909608b51f235d973703d5b7927b13b3c181cf..b24264f237354e9974f6b2fdcc214a321e1db0a1 100644
--- a/media/base/pipeline.h
+++ b/media/base/pipeline.h
@@ -22,6 +22,7 @@
 namespace media {
 
 class Demuxer;
+class DemuxerStream;
 class Renderer;
 class VideoFrame;
 
@@ -75,6 +76,10 @@ class MEDIA_EXPORT Pipeline {
                      Client* client,
                      const PipelineStatusCB& seek_cb) = 0;
 
+  // Restarts playback of the given demuxer |stream| from the |time| position.
+  virtual void RestartStreamPlayback(DemuxerStream* stream,
+                                     base::TimeDelta time) = 0;

[xhwang, 2016/06/04 00:09:43]

What if our current media time is at t1, and |time| != t1. What is the Pipeline
supposed to do?

[servolk, 2016/06/09 21:00:13]

Well, I suppose if we move the 'resume playback' logic deeper into
PipelineController or Pipeline as discussed in other comments, then we won't
need to pass |time| here explicitly and can pass just a set of track ids and
their status.

+
   // Stops the pipeline. This is a blocking function.
   // If the pipeline is started, it must be stopped before destroying it.
   // It it permissible to call Stop() at any point during the lifetime of the