Roll Observatory packages and add a roll script

packages/watcher/test/file_watcher/polling_test.dart

+// Copyright (c) 2015, 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.
+
+@TestOn('linux || mac-os')
+
+import 'package:scheduled_test/scheduled_test.dart';
+import 'package:watcher/watcher.dart';
+
+import 'shared.dart';
+import '../utils.dart';
+
+void main() {
+  watcherFactory = (file) => new PollingFileWatcher(file,
+      pollingDelay: new Duration(milliseconds: 100));
+
+  setUp(() {
+    createSandbox();
+    writeFile("file.txt");
+  });
+
+  sharedTests();
+}