Fix bug in pkg:observe (observable_list.remove(Object))

pkg/observe/test/observable_list_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:observe/observe.dart';
 import 'package:unittest/unittest.dart';
 import 'utils.dart';
 
 main() {
   // TODO(jmesserly): need all standard List API tests.
@@ skipping 13 matching lines @@
       });
     });
 
     test('add changes length', () {
       list.add(4);
       expect(list, [1, 2, 3, 4]);
       deliverChangeRecords();
       expectChanges(changes, [_lengthChange]);
     });
 
+    test('removeObject', () {
+      list.remove(2);
+      expect(list, orderedEquals([1, 3]));
+
+      deliverChangeRecords();
+      deliverChangeRecords();
+      expectChanges(changes, [_lengthChange]);
+    });
+
     test('removeRange changes length', () {
       list.add(4);
       list.removeRange(1, 3);
       expect(list, [1, 4]);
       deliverChangeRecords();
       expectChanges(changes, [_lengthChange]);
     });
 
     test('length= changes length', () {
       list.length = 5;
@@ skipping 192 matching lines @@
     });
   });
 }
 
 const _LENGTH = const Symbol('length');
 
 final _lengthChange = new PropertyChangeRecord(_LENGTH);
 
 _change(index, {removedCount: 0, addedCount: 0}) => new ListChangeRecord(
     index, removedCount: removedCount, addedCount: addedCount);