Implement disabling and enabling media tracks

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index 09bffdaf9ee68f60e24df1d7900a8d64ece510b4..6ce6504717f60cb122f544eff57c2530c0d6301e 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -111,6 +111,8 @@ class FFmpegDemuxerStream : public DemuxerStream {
   AudioDecoderConfig audio_decoder_config() override;
   VideoDecoderConfig video_decoder_config() override;
   VideoRotation video_rotation() override;
+  bool enabled() const override;
+  void set_enabled(bool enabled, base::TimeDelta timestamp) override;
 
   void SetLiveness(Liveness liveness);
 
@@ -172,6 +174,7 @@ class FFmpegDemuxerStream : public DemuxerStream {
   base::TimeDelta last_packet_duration_;
   Ranges<base::TimeDelta> buffered_ranges_;
   VideoRotation video_rotation_;
+  bool is_enabled_;
 
   DecoderBufferQueue buffer_queue_;
   ReadCB read_cb_;