Roll Observatory packages and add a roll script

packages/web_components/test/build/common.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.test.build.common;
+
+// Simple mock of initialize.
+const mockInitialize = '''
+library initialize;
+
+abstract class Initializer<T> {}
+
+class _InitMethod implements Initializer<Function> {
+  const _InitMethod();
+}
+const _InitMethod initMethod = const _InitMethod();''';
+
+// Simple mock of web_components/lib/html_import_annotation.dart
+const mockHtmlImportAnnotation = '''
+library web_components.html_import_annotation;
+
+import 'package:initialize/initialize.dart';
+
+class HtmlImport implements Initializer<LibraryIdentifier> {
+  final String filePath;
+
+  const HtmlImport(this.filePath);
+}''';