Name Test struct's member variables consistently

Change-Id: Ie853618fb496a77ffb79d6669f87048260df68b7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/458979
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed