use GrTextReferenceFrame consistently in SubRuns

Change-Id: I6f221fa3d3df98aeb9a2b955d4d8724a6fb0cc0a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/509136
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed