Apply misc cleanups to mask filter and resource cache

Found these while I was digging into a Chromium rendering change.
The constants have been set for 7+ years now [1] [2].
I prefer how enum classes read and wanted to scope gResourceCache
in the function so we don't access it inappropriately.


[1] http://review.skia.org/170721
[2] https://codereview.chromium.org/2212473002

Change-Id: Ia05d80a74d1abe307400a49ac07dc528389795e3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/939576
Commit-Queue: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
4 files changed