[MCR] Don't require $title to be passed to Revision::newFromId

If the title is not passed in as a param (already known) then select
it in Revision::newFromId instead of waiting for it to be selected
further down the tree.
This means that we can use the same Title object to pass into the
RevisionRecord as well as our legacy Revision object.

The selection chooses either a slave or master depending on
recent writes.

This logic used to be in Revision::getTitle and also in
Revision::newFromConds which was called by newFromId

Bug: T183505
Change-Id: I9cf4ce2c3c86d6bf979a3c88eb423b942b9a1ba4