Revert "Revert "hide nested hinting enum""

This reverts commit 6bd19df9fa9d26d9de4de646b2cdf82ff5dca67c.

Restores original CL, but adds guards for flutter.

Bug: skia:
Change-Id: I380b4ea87d293355026d734249aa2b8c397da144
Reviewed-on: https://skia-review.googlesource.com/c/169345
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
29 files changed