anchor.diff:      }
     }
   
  -  void addAll(Map other) {
  +  void addAll(Map<String, dynamic> other) {
       other.forEach((key, value) {
         this[key] = value;
       });
  
positive.code:     }
    }
  
    void forEach(void f(key, value)) {
      if (_isUpgraded) return _upgradedMap.forEach(f);
      List<String> keys = _computeKeys();
      for (int i = 0; i < keys.length; i++) {
  
negative.code: 
    bool get _isUpgraded => _processed == null;
  
    Map<String, dynamic> get _upgradedMap {
      assert(_isUpgraded);
      // 'cast' the union type to LinkedHashMap.  It would be even better if we
      // could 'cast' to the implementation type, since LinkedHashMap includes
  