/usr/share/gtk-doc/ is in liblightdm-gobject-1-doc 1.2.1-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/gtk-doc/html/
/usr/share/gtk-doc/html/lightdm-gobject-1/
/usr/share/gtk-doc/html/lightdm-gobject-1/core.html
/usr/share/gtk-doc/html/lightdm-gobject-1/home.png
/usr/share/gtk-doc/html/lightdm-gobject-1/index.html
/usr/share/gtk-doc/html/lightdm-gobject-1/index.sgml
/usr/share/gtk-doc/html/lightdm-gobject-1/left.png
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-Greeter-Interface.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-Keyboard-Layout.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-Languages.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-Power-Management.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-Sessions.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-System-Information.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1-User-Accounts.html
/usr/share/gtk-doc/html/lightdm-gobject-1/lightdm-gobject-1.devhelp2
/usr/share/gtk-doc/html/lightdm-gobject-1/right.png
/usr/share/gtk-doc/html/lightdm-gobject-1/style.css
/usr/share/gtk-doc/html/lightdm-gobject-1/up.png