Add support for Mtl backend to DeferredDisplayListTest

Change-Id: Ie576bc8442e5a646c33191100be1be5f89d72290
Reviewed-on: https://skia-review.googlesource.com/c/189483
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed