This code is opted in to the latest language version but was not ever migrated.
It could possibly be just deleted, as it hasn't been runnable for some time, but I have no idea really.
Change-Id: I7ccda121dcd56ed9388b48c70e3b3c0b2d087e47
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/292042
Commit-Queue: Jake Macdonald <jakemac@google.com>
Auto-Submit: Jake Macdonald <jakemac@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>