/usr/share/doc/libgtk-3-0-dbg/changelog.Debian.gz is in libgtk-3-0-dbg 3.18.9-1ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtk-3-0-dbg/../libgtk-3-0/changelog.Debian.gz
/usr/share/doc/libgtk-3-0-dbg/../libgtk-3-0/changelog.Debian.gz