Always force GPU generated masks be top left

Bug: 878195
Change-Id: Ie5e89753c2251ee1b4bd60ac2b02cedb7f5292f7
Reviewed-on: https://skia-review.googlesource.com/150133
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed