DM: move skiatest functions into separate file.

Motivation: allows reuse.

Change-Id: I5732305a213acd83de4ba4e84e0ae27d094cf649
Reviewed-on: https://skia-review.googlesource.com/57241
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
3 files changed