[infra] Add Config.PathToSkia

This should help with non-skia.git repos which use gen_tasks_logic.

Change-Id: I84bf101554555dd42e9349c93aec39280b7de84f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377837
Reviewed-by: Weston Tracey <westont@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
3 files changed