Roll Observatory packages and add a roll script

packages/web_components/e2e_test/html_imports/test/basic_test.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.
+@HtmlImport('packages/html_imports/theme.html')
+library e2e_test.html_imports.basic_test;
+
+import 'dart:html';
+import 'package:initialize/initialize.dart' as init;
+import 'package:web_components/html_import_annotation.dart';
+import 'package:unittest/html_config.dart';
+import 'package:unittest/unittest.dart';
+
+main() {
+  useHtmlConfiguration();
+
+  // Waits until all html imports are loaded.
+  init.run().then((_) {
+    test('text is red', () {
+      var p = document.createElement('p');
+      document.body.append(p);
+      expect(p.getComputedStyle().color, 'rgb(255, 0, 0)');
+    });
+  });
+}