add util for checker image

Change-Id: I6fcf6263a6a261016cb5971872c2f2b5a9943d8e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/341004
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed