Roll Observatory packages and add a roll script

packages/analyzer/lib/src/plugin/command_line_plugin.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 analyzer.src.plugin.command_line_plugin;
 
 import 'package:analyzer/plugin/command_line.dart';
 import 'package:plugin/plugin.dart';
 
 /**
@@ skipping 82 matching lines @@
    * valid result processor.
    */
   void _validateResultProcessorExtension(Object extension) {
     if (extension is! ArgResultsProcessor) {
       String id = resultProcessorExtensionPoint.uniqueIdentifier;
       throw new ExtensionError(
           'Extensions to $id must be an ArgResultsProcessor');
     }
   }
 }