/etc/apparmor.d/abstractions/dbus-accessibility is in apparmor 2.12-4ubuntu5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | # vim:syntax=apparmor
# ------------------------------------------------------------------
#
#    Copyright (C) 2013 Canonical Ltd.
#
#    This program is free software; you can redistribute it and/or
#    modify it under the terms of version 2 of the GNU General Public
#    License published by the Free Software Foundation.
#
# ------------------------------------------------------------------
  # This abstraction grants full accessibility bus access. Consider using the
  # dbus-accessibility-strict abstraction for fine-grained bus mediation.
  #include <abstractions/dbus-accessibility-strict>
  dbus bus=accessibility,
 |