EventListeners defined as classes implementing a call method cannot be used in dart:html
Elsewhere in the system implementing a call method is just as good as implementing a function interface.

Repro:

import 'dart:html';

class MyEventListener {
  call(someEvent) {
    print("I was called");
  }
}

void main() {
  var listener = new MyEventListener();
  print("$listener is an EventListener? ${(listener is EventListener)}");
  window.onResize.listen(listener);
}

Output:
Instance of 'MyEventListener' is an EventListener? true

Exception: Not a Dart closure passed Window.dart:127
Window.$dom_addEventListener Window.dart:127
_EventStreamSubscription._tryResume EventStreamProvider.dart:58
_EventStreamSubscription._EventStreamSubscription EventStreamProvider.dart:23
_EventStream.listen EventStreamProvider.dart:12
main sunflower.dart:93