Roll Observatory packages and add a roll script

packages/web_components/lib/polyfill.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.
 
 /** Dart APIs for interacting with the JavaScript Custom Elements polyfill. */
 library web_components.polyfill;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
@@ skipping 41 matching lines @@
  * Synchronously trigger evaluation of pending lifecycle events, which otherwise
  * need to wait for a [MutationObserver] to signal the changes in the polyfill.
  * This method can be used to resolve differences in timing between native and
  * polyfilled custom elements.
  */
 void customElementsTakeRecords([Node node]) {
   var customElements = js.context['CustomElements'];
   if (customElements == null) return;
   customElements.callMethod('takeRecords', [node]);
 }