Roll Observatory packages and add a roll script

packages/observe/benchmark/test_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 TestObservable extends Observable {
+  @observable int a = 0;
+  @observable int b = 0;
+  @observable int c = 0;
+  @observable int d = 0;
+  @observable int e = 0;
+  @observable int f = 0;
+  @observable int g = 0;
+  @observable int h = 0;
+  @observable int i = 0;
+  @observable int j = 0;
+  @observable int k = 0;
+  @observable int l = 0;
+  @observable int m = 0;
+  @observable int n = 0;
+  @observable int o = 0;
+}