Roll Observatory packages and add a roll script

packages/package_config/lib/discovery_analysis.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.
 
 /// Analyse a directory structure and find packages resolvers for each
 /// sub-directory.
 ///
 /// The resolvers are generally the same that would be found by using
 /// the `discovery.dart` library on each sub-directory in turn,
 /// but more efficiently and with some heuristics for directories that
@@ skipping 146 matching lines @@
     return true;
   }
 }
 
 Packages _loadPackagesFile(File file) {
   var uri = new Uri.file(file.path);
   var bytes = file.readAsBytesSync();
   var map = pkgfile.parse(bytes, uri);
   return new MapPackages(map);
 }