Returns a Future that completes once all buffered data is accepted by the to underlying StreamConsumer.
It's an error to call this method, while an addStream is incomplete.
NOTE: This is not necessarily the same as the data being flushed by the operating system.
Source
/**
* Returns a [Future] that completes once all buffered data is accepted by the
* to underlying [StreamConsumer].
*
* It's an error to call this method, while an [addStream] is incomplete.
*
* NOTE: This is not necessarily the same as the data being flushed by the
* operating system.
*/
Future flush();