/usr/share/accountsservice/interfaces/com.canonical.indicator.sound.AccountsService.xml is in indicator-sound 12.10.2+16.04.20160406-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/accountsservice/interfaces/../../dbus-1/interfaces/com.canonical.indicator.sound.AccountsService.xml