Update SourceBufferStream and its unit tests to always expect valid durations.

media/filters/ffmpeg_demuxer.cc

Index: media/filters/ffmpeg_demuxer.cc
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index e23116f55fedc8d537a3ea7e69b01dc6211f5aa7..afc9fc5c0c615344c6f2f77780113ba068ec75b2 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -278,8 +278,14 @@ void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
       buffer->set_decrypt_config(decrypt_config.Pass());
   }
 
-  buffer->set_duration(
-      ConvertStreamTimestamp(stream_->time_base, packet->duration));
+  if (packet->duration >= 0) {
+    buffer->set_duration(
+        ConvertStreamTimestamp(stream_->time_base, packet->duration));
+  } else {
+    DVLOG(1) << "FFmpeg returned a buffer with a negative duration! "

[acolwell GONE FROM CHROMIUM, 2014/07/16 18:17:46]

Filed https://code.google.com/p/chromium/issues/detail?id=394418 to track down
why FFmpeg is doing this.

[wolenetz, 2014/07/16 19:51:03]

nit: That bug is irksome. Please add a TODO(wolenetz) here referencing that bug;
I think I'll take a look at this during some upcoming ffmpeg work.

[acolwell GONE FROM CHROMIUM, 2014/07/16 19:54:55]

Done.

+             << packet->duration;
+    buffer->set_duration(kNoTimestamp());
+  }
 
   // Note: If pts is AV_NOPTS_VALUE, stream_timestamp will be kNoTimestamp().
   const base::TimeDelta stream_timestamp =