anchor.diff:      if (ourEvent is PointerInputEvent) {
         _handlePointerInputEvent(ourEvent);
       } else {
  +      assert(event.type == 'back');
         for (EventListener listener in _eventListeners)
           listener(ourEvent);
       }
  
positive.code: import 'hit_test.dart';
  import 'object.dart';
  import 'view.dart';
  
  int _hammingWeight(int value) {
    if (value == 0)
  
negative.code:   }
    return weight;
  }
  
  /// A hit test entry used by [FlutterBinding]
  class BindingHitTestEntry extends HitTestEntry {
  