This reverts commit 9292afa710.
Reason for revert: b/244407576
Original change's description:
> Make `addStream` events be delivered synchronously.
>
> The asynchronous stream controllers were forwarding stream events
> from an `addStream` stream through the same path as user-added event,
> which added an extra asynchronous delay that is unnecessary for forwarding existing events.
>
> Change-Id: I8edd1936d0d155d051d3cb8f7f82c577334d5f8e
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/256560
> Reviewed-by: Nate Bosch <nbosch@google.com>
> Commit-Queue: Lasse Nielsen <lrn@google.com>
# Not skipping CQ checks because original CL landed > 1 day ago.
Change-Id: I0e4791f4d32616fee9772a2ab7015bac4e117312
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/257080
Auto-Submit: Ivan Inozemtsev <iinozemtsev@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
Reviewed-by: Ivan Inozemtsev <iinozemtsev@google.com>
