Roll Observatory packages and add a roll script

packages/polymer/lib/src/initializers.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.
 part of polymer;
 
 /// Automatically registers a polymer element.
 class CustomTag implements Initializer<Type> {
   final String tagName;
   const CustomTag(this.tagName);
 
   @override
   initialize(Type t) => Polymer.register(tagName, t);
 }
 
 /// Calls a zero argument [Function] after [Polymer.onReady] completes.
 typedef dynamic _ZeroArg();
 class _WhenPolymerReady implements Initializer<_ZeroArg> {
   const _WhenPolymerReady();
 
   @override
   void initialize(_ZeroArg f) {
     Polymer.onReady.then((_) => f());
   }
 }
 
 const whenPolymerReady = const _WhenPolymerReady();