Registers the given callback in this zone.
It is good practice to register asynchronous or delayed callbacks before invoking run. This gives the zone a chance to wrap the callback and to store information with the callback. For example, a zone may decide to store the stack trace (at the time of the registration) with the callback.
Returns a potentially new callback that should be used in place of the
given callback.
Source
ZoneCallback/*<R>*/ registerCallback/*<R>*/(/*=R*/ callback());