The purpose of the input device descriptor is to make it possible
to associate persistent settings for each input device, such as the
keyboard layout.
The descriptor is a hash of the information we have about the
device, such as its vendor id, product id, unique id, name,
or location.
Bug: 6110399
Change-Id: Idb80f946819b3f0dbf4e661bb0a753dbc2b60981