Fix CurrentUser reference on merge thread

The merge thread was running ChangeMail to send out messages,
but that may need to run queries with the visibleto: predicate,
which incorrectly relied on the ChangeControl.Factory.  Using the
GenericFactory instead permits us to get the ChangeControl for a
given user without needing a current user on the calling thread.

Change-Id: I9eb83b4f04665042182b37c4951966d1540248ff
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed