Roll Observatory packages and add a roll script

packages/unittest/test/testcases_immutable_test.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 unittest.testcases_immutable;
+
+import 'package:unittest/unittest.dart';
+
+import 'package:metatest/metatest.dart';
+
+void main() => initTests(_test);
+
+void _test(message) {
+  initMetatest(message);
+
+  expectTestsPass('testcases immutable', () {
+    test('test', () {
+      expect(() => testCases.clear(), throwsUnsupportedError);
+      expect(() => testCases.removeLast(), throwsUnsupportedError);
+    });
+  });
+}