Returns a String that is an identifier for the represented device that
is persisted across sessions. It is un-guessable by other applications
and unique to the origin of the calling application. It is reset when
the user clears cookies (for Private Browsing, a different identifier
is used that is not persisted across sessions).
Returns a String that is a group identifier. Two devices have the same
group identifier if they belong to the same physical device
— for example a monitor with both a built-in camera and a microphone.