Initialize renderability in GrMockOptions Change-Id: I30a042a41991a47ff1a4e008b88431b4767453dd Reviewed-on: https://skia-review.googlesource.com/c/skia/+/205496 Reviewed-by: Robert Phillips <robertphillips@google.com> Commit-Queue: Brian Osman <brianosman@google.com>