When we moved to make errors non-nullable in the async API, I added
legacy tests, but not NNBD tests because it is a static error in NNBD.
However, we've since started testing that null is caught dynamically
when flowing into those APIs from legacy code.
So this migrates those tests over.
Change-Id: I8002bacb45e947ef8c93dca10c7c1fd41afaa696
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152614
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>