Roll Observatory packages and add a roll script

packages/plugin/lib/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 plugin;
 
 /**
  * A function used to register the given [extension] to the extension point with
  * the given unique [identifier].
  *
@@ skipping 110 matching lines @@
   static String buildUniqueIdentifier(Plugin plugin, String simpleIdentifier) =>
       join(plugin.uniqueIdentifier, simpleIdentifier);
 
   /**
    * Return an identifier created by joining the [pluginIdentifier] and the
    * [simpleIdentifier].
    */
   static String join(String pluginIdentifier, String simpleIdentifier) =>
       '$pluginIdentifier.$simpleIdentifier';
 }