Roll Observatory packages and add a roll script

packages/charted/lib/charts/chart_events.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 84 matching lines @@
   ///    chart.  Behaviors can use it to draw any visualization in response
   ///    to user actions.
   ///  - [lowerRenderPane] is the Selection that is rendered below the chart.
   void init(
       ChartArea area, Selection upperRenderPane, Selection lowerRenderPane);
 
   /// Clears all DOM created by this behavior, unsubscribes to event listeners
   /// and clears any state.
   void dispose();
 }