Make the timestamp unroll offset consistent accross PES pids.

media/formats/mp2t/mp2t_stream_parser.h

Index: media/formats/mp2t/mp2t_stream_parser.h
diff --git a/media/formats/mp2t/mp2t_stream_parser.h b/media/formats/mp2t/mp2t_stream_parser.h
index e419f029ae54d44f1f3a3060aa969e921b45536c..57abb0c7a91938685db9037c00e1964da1fc95a4 100644
--- a/media/formats/mp2t/mp2t_stream_parser.h
+++ b/media/formats/mp2t/mp2t_stream_parser.h
@@ -15,6 +15,7 @@
 #include "media/base/media_export.h"
 #include "media/base/stream_parser.h"
 #include "media/base/video_decoder_config.h"
+#include "media/formats/mp2t/timestamp_unroller.h"
 
 namespace media {
 
@@ -123,6 +124,14 @@ class MEDIA_EXPORT Mp2tStreamParser : public StreamParser {
 
   // Indicate whether a segment was started.
   bool segment_started_;
+
+  // Timestamp unroller.
+  // Timestamps in PES packets must be unrolled using the same offset.
+  // So the unroller is global between PES pids.
+  TimestampUnroller timestamp_unroller_;
+
+  // The timestamp unroller might create negative timestamps,
+  // we need to add a time offset to make sure all timestamps are positive.
   base::TimeDelta time_offset_;
 
   DISALLOW_COPY_AND_ASSIGN(Mp2tStreamParser);