[graphite] Restore temporary getter to silence compiler unused member warning

I am a clown and prematurely deleted the temporary workaround from https://skia-review.googlesource.com/c/skia/+/615878. This is what happens when you juggle multiple CLs at once. Let this be a cautionary tale...

Change-Id: I1a2abc484a23a7d7d0a9ae56e7961cc8a5ecb7bc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/617642
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
1 file changed