Roll Observatory packages and add a roll script

packages/web_components/lib/transformer.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.
 
 /// Transformer used for pub serve and pub build
 library web_components.transformer;
 
 import 'package:barback/barback.dart';
 
 export 'build/html_import_annotation_recorder.dart';
@@ skipping 102 matching lines @@
     error = false;
   } else {
     error = true;
   }
   if (error) {
     print('Bad value for "entry_points" in the web_components transformer. '
         'Expected either one String or a list of Strings.');
   }
   return files;
 }