package:observe fix various api issues

samples/third_party/todomvc/web/model.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 todomvc.web.model;
 
 import 'package:polymer/polymer.dart';
 
 final appModel = new AppModel._();
 
 @reflectable
-class AppModel extends ObservableBase {
+class AppModel extends Observable {
   final ObservableList<Todo> todos = new ObservableList<Todo>();
   @observable int doneCount;
   @observable int remaining;
   @observable List<Todo> visibleTodos;
   @observable bool hasCompleteTodos;
 
   bool _allChecked;
 
   AppModel._() {
     new ListPathObserver(todos, 'done').changes.listen(_updateTodoDone);
@@ skipping 29 matching lines @@
 
   // TODO(jmesserly): the @observable here is temporary.
   bool get allChecked => _allChecked;
   set allChecked(bool value) {
     todos.forEach((t) { t.done = value; });
   }
 
   void clearDone() => todos.removeWhere((t) => t.done);
 }
 
-class Todo extends ObservableBase {
+class Todo extends Observable {
   @observable String task;
   @observable bool done = false;
 
   Todo(this.task);
 
   String toString() => "$task ${done ? '(done)' : '(not done)'}";
 }