add some api helpers (extracted from different CL)

See https://skia-review.googlesource.com/c/skia/+/253996/

Change-Id: I06cb3cb6dc8c088f139e6f2a78e43069c2609ff0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254736
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
3 files changed