Enable round-tripping and updating of WebSourceBufferImpl timestamp offset

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 857dcfd3e6c607c7aaf1bdbac356272d2e5f8e65..7463bcdc144c53215227f20ed98bc20cd11b32fb 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -124,6 +124,12 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   // middle of parsing a media segment.
   bool SetTimestampOffset(const std::string& id, base::TimeDelta offset);
 
+  // Retrieves the current offset being applied to subsequent buffers appended
+  // to the source buffer associated with |id|. If the implementation has not
+  // changed the offset since construction or the last SetTimestampOffset(),
+  // returns kNoTimestamp() instead to indicate it has not been updated.
+  base::TimeDelta GetUpdatedTimestampOffset(const std::string& id);
+
   // Set the append mode to be applied to subsequent buffers appended to the
   // source buffer associated with |id|. If |sequence_mode| is true, caller
   // is requesting "sequence" mode. Otherwise, caller is requesting "segments"