workaround for buggy macOS GLSL shader compiler

Bug: skia:
Change-Id: Ib77e11d80f93f76e65eac6119dbf2bd03523aaf9
Reviewed-on: https://skia-review.googlesource.com/117626
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
2 files changed