Roll Observatory packages and add a roll script

packages/charted/lib/charts/src/cartesian_area_impl.dart

 //
 // Copyright 2014 Google Inc. All rights reserved.
 //
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 //
 
 part of charted.charts;
 
@@ skipping 720 matching lines @@
           _series.renderer.onValueMouseOver.listen(_mouseOver),
           _series.renderer.onValueMouseOut.listen(_mouseOut)
         ]);
       }
     }
     _renderer = _series.renderer;
   }
 
   dispose() => _disposer.dispose();
 }