MSE: Record counts of detected MSE audio, video and text tracks

media/filters/chunk_demuxer.h

Index: media/filters/chunk_demuxer.h
diff --git a/media/filters/chunk_demuxer.h b/media/filters/chunk_demuxer.h
index 677fa2a41cff9bee3114f9e7f46872b887899e44..fa7540dc4d5dcfa26bcba41b805d0e33019e0c7a 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -405,6 +405,11 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   // Indicates that splice frame generation is enabled.
   const bool splice_frames_enabled_;
 
+  // Accumulate, by type, detected track counts across the SourceBuffers.
+  int detected_audio_track_count_;
+  int detected_video_track_count_;
+  int detected_text_track_count_;
+
   DISALLOW_COPY_AND_ASSIGN(ChunkDemuxer);
 };