This class, introduced in SERVER-40809, has two purposes:

• cache the CollectionPtr to the oplog collection; and
• to help reserve optimes for timestamped writes.

It uses the ReplicationCoordinator only to retrieve the current term to populate the optimes it returns.

This class may be more relevant to correct catalog operation than any specific replica set functionality. We can make a case for moving this class from db/repl to db/catalog.