Fix TSAN bug in TransferPixelsTest

Change-Id: I067d9e86d00ab6bfa91e2d22725b26315a3ec348
Reviewed-on: https://skia-review.googlesource.com/144026
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed