Roll Observatory packages and add a roll script

packages/charted/lib/charts/src/layout_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;
 
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   @override
   void removeChartBehavior(ChartBehavior behavior) {
     if (behavior == null || !_behaviors.contains(behavior)) return;
     if (upperBehaviorPane != null && lowerBehaviorPane != null) {
       behavior.dispose();
     }
     _behaviors.remove(behavior);
   }
 }