Internalize color offset calculation to SubRun

Change-Id: I76f57a11c66c708462e4c91cc5cf8967d60b78c5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261442
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: Herb Derby <herb@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed