Roll Observatory packages and add a roll script

packages/initialize/lib/build/loader_replacer.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 initialize.build.loader_replacer;
 
 import 'dart:async';
 import 'package:barback/barback.dart';
 
 /// Removes `mirror_loader.dart` and replaces it with `static_loader.dart`.
 class LoaderReplacer extends Transformer {
   LoaderReplacer.asPlugin();
 
   bool isPrimary(AssetId id) =>
       id.package == 'initialize' && id.path == 'lib/initialize.dart';
 
   Future apply(Transform transform) {
     var id = transform.primaryInput.id;
     return transform.primaryInput.readAsString().then((code) {
       transform.addOutput(new Asset.fromString(
           id, code.replaceFirst('mirror_loader.dart', 'static_loader.dart')));
     });
   }
 }