MATE support was incomplete in b961235b197647d6649ef3d48d7cc2cecafe3d47
it did not add support for xdg-settings which Google Chrome/Chromium
uses to detect and set default browser.
MATE 1.5 uses same schema as gnome3, so shortcut to gnome3 methods
$ xdg-settings get default-web-browser
$ xdg-settings check
patch raw address: https://raw.github.com/pld-linux/xdg-utils/d00c89c373952fc89dc6179ad327785236a54782/0001-xdg-settings-add-MATE-support.patch