Roll Observatory packages and add a roll script

web_components/lib/custom_element_proxy.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.
-library web_components.custom_element_proxy;
-
-import 'dart:js' as js;
-import 'package:initialize/initialize.dart';
-import 'interop.dart';
-
-/// Annotation for a dart class which proxies a javascript custom element.
-/// This will not work unless `interop_support.js` is loaded.
-// TODO(jakemac): Add an @HtmlImport here to a new file which includes
-// `interop_support.js`. We will need to point everything else at that html file
-// as well for deduplication purposes (could even just copy it in as an inline
-// script so the js file no longer exists?).
-class CustomElementProxy implements Initializer<Type> {
-  final String tagName;
-  final String extendsTag;
-
-  const CustomElementProxy(this.tagName, {this.extendsTag});
-
-  void initialize(Type t) {
-    registerDartType(tagName, t, extendsTag: extendsTag);
-  }
-}
-
-/// A simple mixin to make it easier to interoperate with the Javascript API of
-/// a browser object. This is mainly used by classes that expose a Dart API for
-/// Javascript custom elements.
-class CustomElementProxyMixin {
-  js.JsObject _proxy;
-
-  js.JsObject get jsElement {
-    if (_proxy == null) {
-      _proxy = new js.JsObject.fromBrowserObject(this);
-    }
-    return _proxy;
-  }
-}