/usr/lib/libevent_extra.so is in libevent1-dev 1.4.14b-stable-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libevent_extra-1.4.so.2.2.0
/usr/lib/libevent_extra-1.4.so.2.2.0