Roll Observatory packages and add a roll script

packages/csslib/lib/src/polyfill.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.
 
 part of csslib.parser;
 
 /**
  * CSS polyfill emits CSS to be understood by older parsers that which do not
  * understand (var, calc, etc.).
  */
@@ skipping 236 matching lines @@
       }
     } else {
       // Return real CSS property.
       return varDef;
     }
   }
 
   // Didn't point to a var definition that existed.
   return varDef;
 }