fix gm to test unpremul etc.

Change-Id: Ia53003e31b2e24ffc5834faefb1de0687036683d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270057
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed