Roll Observatory packages and add a roll script

packages/polymer_interop/lib/src/polymer_proxy_mixin.dart

 // Copyright (c) 2014, 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 polymer_interop.src.js_element_proxy;
 
 import 'dart:html' show Element, DocumentFragment;
 import 'dart:js' as js;
 import 'package:web_components/web_components.dart'
     show CustomElementProxyMixin;
 
@@ skipping 43 matching lines @@
   /// deactivate the element's bindings and allow its memory to be reclaimed.
   void unbindAll() => jsElement.callMethod('unbindAll', []);
 
   /// Call in `detached` to prevent the element from unbinding when it is
   /// detached from the dom. The element is unbound as a cleanup step that
   /// allows its memory to be reclaimed. If `cancelUnbindAll` is used, consider
   ///calling `unbindAll` when the element is no longer needed. This will allow
   ///its memory to be reclaimed.
   void cancelUnbindAll() => jsElement.callMethod('cancelUnbindAll', []);
 }