Make PrimitiveProcessorTest's op be a non-legacy GrMeshDrawOp

Change-Id: I14c03c350e43dd576904d94a9f0847405dedd0a6
Reviewed-on: https://skia-review.googlesource.com/23142
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed