An event% object contains information about a control,
keyboard, mouse, or scroll event. See also
control-event%,
key-event%,
mouse-event%, and
scroll-event%.
constructor
time-stamp : exact-integer? = 0 
See get-time-stamp for information about
 time-stamp.
method
(send an-event get-time-stamp) → exact-integer?
Returns the time, in milliseconds, when the event occurred. This time
 is compatible with times reported by Racket’s
 current-milliseconds procedure.
method
(send an-event set-time-stamp time) → void?
time : exact-integer? 
Set the time, in milliseconds, when the event occurred. See also
 Racket’s current-milliseconds.
If the supplied value is outside the platform-specific range of time
 values, an exn:fail:contract exception is raised.