VisibleRefFilter may need to evaluate visibility for tens of
thousands of refs. Doing tens of thousands of random Changes table
lookups in order to load changes is a nonstarter, so forbid this in
the tests.
We still need to pass a ReviewDb instance as it's required to pass to
ChangeControl which needs to create a ChangeData. But we should be
getting everything we need for the Change from the secondary index.
So use a DisabledReviewDb.
Change-Id: I369b1aa7612400a0c36844702d551d6676b6c691
df4868f382