Roll Observatory packages and add a roll script

packages/csslib/lib/src/messages.dart

 // Copyright (c) 2012, 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 csslib.src.messages;
 
 import 'package:logging/logging.dart' show Level;
 import 'package:source_span/source_span.dart';
 
 import 'options.dart';
@@ skipping 110 matching lines @@
   }
 
   /** Merge [newMessages] to this message lsit. */
   void mergeMessages(Messages newMessages) {
     messages.addAll(newMessages.messages);
     newMessages.messages
         .where((message) => message.level == Level.SEVERE || options.verbose)
         .forEach(printHandler);
   }
 }