/usr/share/mate-panel/ is in ubuntu-mate-default-settings 16.04.5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/mate-panel/layouts/
/usr/share/mate-panel/layouts/eleven-fresh.layout
/usr/share/mate-panel/layouts/eleven-indicators-fresh.layout
/usr/share/mate-panel/layouts/eleven-indicators.layout
/usr/share/mate-panel/layouts/eleven.layout
/usr/share/mate-panel/layouts/mutiny-fresh.layout
/usr/share/mate-panel/layouts/mutiny-fresh.panel
/usr/share/mate-panel/layouts/mutiny-indicators-fresh.layout
/usr/share/mate-panel/layouts/mutiny-indicators-fresh.panel
/usr/share/mate-panel/layouts/mutiny-indicators.layout
/usr/share/mate-panel/layouts/mutiny-indicators.panel
/usr/share/mate-panel/layouts/mutiny.layout
/usr/share/mate-panel/layouts/mutiny.panel
/usr/share/mate-panel/layouts/netbook-fresh.layout
/usr/share/mate-panel/layouts/netbook-indicators-fresh.layout
/usr/share/mate-panel/layouts/netbook-indicators.layout
/usr/share/mate-panel/layouts/netbook.layout
/usr/share/mate-panel/layouts/redmond-fresh.layout
/usr/share/mate-panel/layouts/redmond-indicators-fresh.layout
/usr/share/mate-panel/layouts/redmond-indicators.layout
/usr/share/mate-panel/layouts/redmond.layout
/usr/share/mate-panel/layouts/ubuntu-mate-fresh.layout
/usr/share/mate-panel/layouts/ubuntu-mate-indicators-fresh.layout
/usr/share/mate-panel/layouts/ubuntu-mate-indicators.layout
/usr/share/mate-panel/layouts/ubuntu-mate.layout