Update charted to 0.4.8 and roll

packages/observe/benchmark/test_path_observable.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 observe.test.benchmark.test_observable;
-
-import 'package:observe/observe.dart';
-
-class Bar extends Observable {
-  @observable int baz;
-
-  Bar(this.baz);
-}
-
-class Foo extends Observable {
-  @observable Bar bar;
-
-  Foo(int value) : bar = new Bar(value);
-}
-
-class TestPathObservable extends Observable {
-  @observable Foo foo;
-
-  TestPathObservable(int value) : foo = new Foo(value);
-}