Switch MDB GrContextOptions over to Enable style

Change-Id: Id6541c346a13649c89ca3b9ccb13972976f9b973
Reviewed-on: https://skia-review.googlesource.com/105603
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
8 files changed