For some operations in Gerrit we perform a reachability check. The
majority of checks is fine with just checking if the commit is reachable
from refs/heads/* or refs/tags/* but CommitsCollection requires some
more places to be included like refs/meta/dashboards or refs/users/*.
However, it does not require refs/changes/* to be included in the check
because we have already checked if the commit is reachable by a change
(= is the commit of a change). This check also covers stacked changes as
we have one change per commit in the stack.
There is no case where the parent of a change is neither another change
nor part of a ref that can be reached through refs/heads/* or
refs/tags/*. Therfore we spare reevaluating change refs where possible.
Change-Id: Icba91f7c770863d34c920320e944e8f2e86783e1
6b7c8ab89a