Roll Observatory packages and add a roll script

packages/charted/lib/charts/src/chart_legend_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;
 
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             }
           });
     }
 
     rows.exit.remove();
   }
 
   /// Update legend to show chart's selection and visibility.
   void _handleStateChanges(_) => _createLegendItems();
 }