/usr/share/unity-control-center/keybindings/50-metacity-navigation.xml is in metacity-common 1:3.18.3-1ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/unity-control-center/keybindings/../../gnome-control-center/keybindings/50-metacity-navigation.xml