expand gm to test GPU and CPU

Change-Id: I7d1c80f1b7dadc8535736385aa3adb935fa24293
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271237
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed