Update duration when demuxed packets exceed known duration.

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 65756447daa73aa4ed97938974bdacbcb53c2ac2..6a04804fdae446454a9f147a20756e9795ea15e9 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -353,6 +353,7 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
   // Set if we know duration of the audio stream. Used when processing end of
   // stream -- at this moment we definitely know duration.
   bool duration_known_;
+  base::TimeDelta duration_;
 
   // FFmpegURLProtocol implementation and corresponding glue bits.
   std::unique_ptr<BlockingUrlProtocol> url_protocol_;