This is a strong mode migration that was missed in the earlier rounds.
It allows use of functions that have a more restricted argument type than Object in strong mode
while still ensuring that the argument has a correct type.
Change-Id: Ib00e3f4b4a679c003a992d674c36ef672729b22e
Reviewed-on: https://dart-review.googlesource.com/24540
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Leaf Petersen <leafp@google.com>