Demoting a variable back to its declared type discards types of
interest, therefore in order to verify that a type is of interest, we
need to join a demoting path with a non-demoting path so that the type
of interest is preserved.
Change-Id: Ie9c3278936b189120c9f0085f1563ff8062e51db
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164800
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Leaf Petersen <leafp@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Paul Berry