In a notedb world we would like to slurp all information about a
change from the git-based storage as soon as a ChangeResource is
constructed, which will involve extra work in this parse, analogous to
how parse currently validates the change permissions.
Preserve the ability to pass in a particular ChangeControl object,
since various callers have specific requirements like reusing the
control elsewhere, or using a control for a different user.
Change-Id: Ia7c9761ef92bb8f05ae3323210babaa02b0dbe6f
fcb204627b