I am running Ubuntu on a Chromebook, and the media key's don't work because Ubuntu treats the keyboard as a regular, generic keyboard with 105 keys.
In MATE Desktop, there is a way to change the keyboard layout (i.e. keyboard model), and so is there in KDE.
(MATE keyboard layout settings)
(KDE's keyboard layout settings)
How to do this in GNOME?
GNOME settings offer me the option to change the layout to that of another language, but not the keyboard model.