anchor.diff:    int get length => _map.length;
     bool get isEmpty => _map.isEmpty;
     bool get isNotEmpty => _map.isNotEmpty;
  +  String toString() => _map.toString();
   }
  
positive.code:           result[str.substring(0, equalsIndex)] =
                str.substring(equalsIndex + 1);
          }
          _environmentCache = new UnmodifiableMapView(result);
        } else {
          _environmentCache = env;
        }
  
negative.code: // Environment variables are case-insensitive on Windows. In order
  // to reflect that we use a case-insensitive string map on Windows.
  class _CaseInsensitiveStringMap<V> implements Map<String, V> {
    final Map<String, V> _map = new Map<String, V>();
  
    bool containsKey(String key) => _map.containsKey(key.toUpperCase());
    bool containsValue(Object value) => _map.containsValue(value);
  