Receives events from source and puts them into this controller's stream.
Returns a future which completes when the source stream is done.
Events must not be added directly to this controller using add, addError, close or addStream, until the returned future is complete.
Data and error events are forwarded to this controller's stream. A done
event on the source will end the addStream operation and complete the
returned future.
If cancelOnError is true, only the first error on source is
forwarded to the controller's stream, and the addStream ends
after this. If cancelOnError is false, all errors are forwarded
and only a done event will end the addStream.
Source
Future addStream(Stream<T> source, {bool cancelOnError: true});