extract ToolUtils::colortype_depth()

Change-Id: I55a3956ed6d0587f72ddff24a1769ab14e25131f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206981
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed