Creates an Observable where all events of an existing stream are piped through a sink-transformation.
mapSink closure is invoked when the returned stream is
listened to. All events from the
source are added into the event sink
that is returned from the invocation. The transformation puts all
transformed events into the sink the
mapSink closure received during
its invocation. Conceptually the
mapSink creates a transformation pipe
with the input sink being the returned EventSink and the output sink
being the sink it received.
factory Observable.eventTransformed( Stream<T> source, EventSink<T> mapSink(EventSink<T> sink)) => Observable<T>((Stream<T>.eventTransformed(source, mapSink)));