Move more virtuals into ...Base to hide them from public api

Bug: skia:12111

Change-Id: I35601e0504e8e1186314e19bf53f01274bfc0ae0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/419357
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
7 files changed