Add APIs for asserting the types of transformers. I thought about adding these to Delegating*Transformer classes, but those delegates don't really make any sense at all on their own, so I found other places instead. R=lrn@google.com Review URL: https://codereview.chromium.org//1947923003 .
Contains utility classes in the style of dart:async to work with asynchronous computations.
The StreamZip class can combine several streams of events into a single stream of tuples of events.
The package introduces a Result class that can hold either a value or an error. It allows capturing an asynchronous computation which can give either a value or an error, into an asynchronous computation that always gives a Result value, where errors can be treated as data. It also allows releasing the Result back into an asynchronous computation.