Roll Observatory packages and add a roll script

web_components/lib/build/mirrors_remover.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.build.mirrors_remover;
-
-import 'dart:async';
-import 'package:barback/barback.dart';
-
-/// Removes `mirror_initializer.dart` and replaces it with
-/// `static_initializer.dart`.
-class MirrorsRemoverTransformer extends Transformer {
-  MirrorsRemoverTransformer();
-  MirrorsRemoverTransformer.asPlugin(BarbackSettings settings);
-
-  bool isPrimary(AssetId id) => id.path == 'lib/src/init.dart';
-
-  @override
-  Future apply(Transform transform) async {
-    String source = await transform.primaryInput.readAsString();
-    source =
-        source.replaceAll('mirror_initializer.dart', 'static_initializer.dart');
-    transform
-        .addOutput(new Asset.fromString(transform.primaryInput.id, source));
-  }
-}