revlog: refactor chain variable Previously the addgroup loop would set chain to be the result of self._addrevision(node,...). Since _addrevision now always returns the passed in node, we can drop that behavior and just always set chain = node in the loop. This will be useful in a future patch where we refactor the cg.deltachunk logic to another function and therefore chain disappears entirely from this function. Differential Revision: https://phab.mercurial-scm.org/D699