The sync operations on a MultiStreamController did not check whether
sending events at the current time was allowed.
That could lead to `null` dereferencing errors when doing operations
on the controller after a cancel, and could cause events to appear
out of order.
Change-Id: I06b86a78959dfcaa402f74e2980a9d515f097dc9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/159442
Reviewed-by: Erik Ernst <eernst@google.com>
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Lasse Reichstein Holst Nielsen
0d322488ae