The ToolUtils file is getting a bit bloated, IMO. I noticed this when
working on Bazel includes.
Including non-header files is a small nuisance in Bazel, so it
is probably better to just make it its own compilation unit.
Change-Id: I06ca3808a37ebef6478f5afa3f14086429899590
Bug: skia:12541
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/459197
Reviewed-by: Ben Wagner <bungeman@google.com>
