The `async*` function `yield` should work well with `await for`.

The `async*` function `yield` is specified to wait until the event has been delivered, giving the receiver time to pause or cancel in (immediate) response to receiving the event.

Implementations do not wait for the receiver. This makes it hard and inefficient to write `async*` functions that do not do too much work.
The implementations should follow the specification and make the user experience better.

Associated [feature specification](https://github.com/dart-lang/language/blob/master/accepted/future-releases/async-star-behavior/feature-specification.md) has more details.