/usr/share/gtk-doc/html/libgnomeui is in libgnomeui-doc 2.24.5-2ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/gtk-doc/html/../../doc/libgnomeui-doc/html
/usr/share/gtk-doc/html/../../doc/libgnomeui-doc/html