enqueue method
Enqueues a Toasted toast. Returns a future that completes the toast is removed from the queue either after it transitions out or when the queue is cleared.
Implementation
Future<void> enqueue(Toasted toast) {
final onDequeued = _onToastDequeued(toast);
_queue.add(toast);
if (_state == ToastedState.none) {
_next();
}
return onDequeued;
}