Roll Observatory packages and add a roll script

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);
+}