Roll Observatory packages and add a roll script

packages/charted/lib/charts/cartesian_renderers/cartesian_base_renderer.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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       }
       if (state.hovered != null && state.hovered.last == row) {
         flags |= ChartState.VAL_HOVERED;
       }
       _valueColorCache[hash] =
           theme.getColorForKey(area.useRowColoring ? row : column, flags);
       _valueFilterCache[hash] = theme.getFilterForState(flags);
     }
   }
 }