Seek for video track changes on FFmpegDemuxer.

media/blink/webmediaplayer_impl.cc

Index: media/blink/webmediaplayer_impl.cc
diff --git a/media/blink/webmediaplayer_impl.cc b/media/blink/webmediaplayer_impl.cc
index 1673e039c862f2d48686e2b17dcfd60f9ec56d00..b69d127921d8febf42a3e9deef95d2d9759f1954 100644
--- a/media/blink/webmediaplayer_impl.cc
+++ b/media/blink/webmediaplayer_impl.cc
@@ -2308,6 +2308,8 @@ void WebMediaPlayerImpl::ReportTimeFromForegroundToFirstFrame(
     base::TimeTicks foreground_time,
     base::TimeTicks new_frame_time) {
   base::TimeDelta time_to_first_frame = new_frame_time - foreground_time;
+  LOG(ERROR) << __func__ << " : " << time_to_first_frame.InMillisecondsF()
+             << "ms";
   if (HasAudio()) {
     UMA_HISTOGRAM_TIMES(
         "Media.Video.TimeFromForegroundToFirstFrame.DisableTrack",