This commit makes RefControl package-private by removing all references
by migrating all callers to PermissionBackend. It makes the following
non-trivial changes:
1) Decompose ref-ownership into READ_CONFIG and WRITE_CONFIG.
WRITE_CONFIG serves as the traditional isOwner() while READ_CONFIG can
be used to check if the user can read the ref config. This defaults to
READ on refs/meta/config for now but can be more specific in the future.
2) Add a new READ_PRIVATE_CHANGES permission to RefPermission to account
for canReadPrivateChanges() and isEditVisible(). This is used for
VisibleRefsFilter.
This commit leaves a TODO for the future on how to treat ref owners in
emails. As of now, we still upgrade owners to 'TO' when they are on
either 'CC' or 'BCC'. This will change in a follow-up change as it is
hard to support on top of a permission backend as it involves many
permission checks on every email sent as well as confusing as internally
we don't have a ref owner anymore.
Change-Id: Ia6fa468dac49588241b52b4451fe79bcf6776077
1851a8b786