write hashes, .pngs optional

Change-Id: Id23bcfab9f6b3faf5742f0797ac5f33e5acd6d53
Reviewed-on: https://skia-review.googlesource.com/c/175760
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
5 files changed