Roll Observatory packages and add a roll script

packages/path/lib/src/style/posix.dart

 // Copyright (c) 2013, 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 path.style.posix;
 
 import '../characters.dart' as chars;
 import '../parsed_path.dart';
 import '../internal_style.dart';
 
@@ skipping 44 matching lines @@
       parsed.parts.addAll(["", ""]);
     } else if (parsed.hasTrailingSeparator) {
       // If the path has a trailing slash, add a single empty component so the
       // URI has a trailing slash as well.
       parsed.parts.add("");
     }
 
     return new Uri(scheme: 'file', pathSegments: parsed.parts);
   }
 }