hide savelayer's clipmask fields

Bug: skia:9208
Change-Id: Ieff64b3132e7bf4a51ce9d70ea2f1bad492616da
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223923
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
12 files changed