/usr/lib/x86_64-linux-gnu/libdbusmenu-gtk3.so is in libdbusmenu-gtk3-dev 12.10.3+14.04.20140319-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdbusmenu-gtk3.so.4.0.12