Make flags private

Change-Id: I16139e8e6479b7088d5b426d4903fe71dd53d4af
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/293376
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed