fix observe tests

pkg/observe/test/list_change_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 'dart:async';
 import 'package:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'observe_test_utils.dart';
 
 // This file contains code ported from:
@@ skipping 250 matching lines @@
       observeArray(model);
       model.addAll([1, 2, 3]);
       assertEditDistance(model, 3);
     });
 
     observeTest('trunacte and add, sharing a contiguous block', () {
       var model = toObservable(['x', 'x', 'x', 'x', '1', '2', '3']);
       observeArray(model);
       model.length = 0;
       model.addAll(['1', '2', '3', 'y', 'y', 'y', 'y']);
-      assertEditDistance(model, 7);
+      assertEditDistance(model, 8);
     });
 
     observeTest('truncate and add, sharing a discontiguous block', () {
       var model = toObservable(['1', '2', '3', '4', '5']);
       observeArray(model);
       model.length = 0;
       model.addAll(['a', '2', 'y', 'y', '4', '5', 'z', 'z']);
-      assertEditDistance(model, 8);
+      assertEditDistance(model, 7);
     });
 
     observeTest('insert at beginning and end', () {
       var model = toObservable([2, 3, 4]);
       observeArray(model);
       model.insert(0, 5);
       model[2] = 6;
       model.add(7);
       assertEditDistance(model, 4);
     });
   });
 }