Add timestampOffset as a parameter to createSegmentReference
Add timestampOffset as a parameter to createSegmentReference

TimestampOffset will be used as a paramater to create the segment
references with discontinuity tags.

Issue #1335

Change-Id: If7dfb63766c2397256561e6668e98f9136f885b5

tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player