Roll Observatory packages and add a roll script

packages/polymer_expressions/example/person.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.
+
+library person;
+
+import 'package:observe/observe.dart';
+
+class Person extends ChangeNotifier {
+  String _firstName;
+  String _lastName;
+  List<String> _items;
+
+  Person(this._firstName, this._lastName, this._items);
+
+  String get firstName => _firstName;
+
+  void set firstName(String value) {
+    _firstName = notifyPropertyChange(#firstName, _firstName, value);
+  }
+
+  String get lastName => _lastName;
+
+  void set lastName(String value) {
+    _lastName = notifyPropertyChange(#lastName, _lastName, value);
+  }
+
+  String getFullName() => '$_firstName $_lastName';
+
+  List<String> get items => _items;
+
+  void set items(List<String> value) {
+    _items = notifyPropertyChange(#items, _items, value);
+  }
+
+  String toString() => "Person(firstName: $_firstName, lastName: $_lastName)";
+}