Roll Observatory packages and add a roll script

packages/package_config/lib/src/packages_impl.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.
 
 /// Implementations of [Packages] that may be used in either server or browser
 /// based applications. For implementations that can only run in the browser,
 /// see [package_config.packages_io_impl].
 library package_config.packages_impl;
 
 import "dart:collection" show UnmodifiableMapView;
@@ skipping 74 matching lines @@
   }
 
   Iterable<String> get packages {
     throw _failListingPackages();
   }
 
   Map<String, Uri> asMap() {
     throw _failListingPackages();
   }
 }