introduce ObservableList.listChanges to keep list changes separate from property changes

pkg/observe/lib/observe.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.
 
 /**
  * Support for observing changes in model-view architectures.
  *
  * **Warning:** This library is experimental, and APIs are subject to change.
  *
  * This library is used to observe changes to [Observable] types. It also
@@ skipping 64 matching lines @@
  * [Tools](https://www.dartlang.org/polymer-dart/) exist to convert the first
  * form into the second form automatically, to get the best of both worlds.
  */
 library observe;
 
 export 'src/bind_property.dart';
 export 'src/change_notifier.dart';
 export 'src/change_record.dart';
 export 'src/compound_path_observer.dart';
 export 'src/list_path_observer.dart';
+export 'src/list_diff.dart' show ListChangeRecord;
 export 'src/metadata.dart';
 export 'src/observable.dart' hide notifyPropertyChangeHelper, objectType;
 export 'src/observable_box.dart';
 export 'src/observable_list.dart';
 export 'src/observable_map.dart';
 export 'src/path_observer.dart';
 export 'src/to_observable.dart';