fix analyzer error in path observer test

pkg/mdv_observe/test/path_observer_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:mdv_observe/mdv_observe.dart';
 import 'package:unittest/unittest.dart';
 
 // This file contains code ported from:
 // https://github.com/rafaelw/ChangeSummary/blob/master/tests/test.js
 
@@ skipping 229 matching lines @@
   getValueWorkaround(key) {
     if (key == fieldName) return value;
     return null;
   }
   void setValueWorkaround(key, newValue) {
     if (key == fieldName) value = newValue;
   }
 
   toString() => '#<$runtimeType $fieldName: $_value>';
 }
-
-_record(key, oldValue, newValue, [kind = ChangeRecord.FIELD]) =>
-    new ChangeRecord(key, oldValue, newValue, kind: kind);