Roll Observatory packages and add a roll script

packages/polymer/lib/src/build/messages.dart

 // Copyright (c) 2014, 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.
 
 /// Contains all error and warning messages produced by polymer.
 library polymer.src.build.messages;
 
 import 'package:code_transformers/messages/messages.dart';
 import 'constants.dart';
 
@@ skipping 608 matching lines @@
 directory. Moving these files to your `lib` folder or specifying all your entry
 points in your configuration will fix this.
 ''');
 
 const MISSING_POLYMER_DART = const MessageTemplate(
     const MessageId('polymer', 48), 'polymer.dart not imported.',
     'polymer.dart not imported.', '''
 It is required that your application contains an import to
 `package:polymer/polymer.dart`.
 ''');