Roll Observatory packages and add a roll script

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')));
-    });
-  }
-}