Roll Observatory packages and add a roll script

packages/charted/lib/charts/behaviors/chart_tooltip.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 181 matching lines @@
 
   FormatFunction _getFormatterForColumn(int column) =>
       _area.data.columns.elementAt(column).formatter;
 
   hide(ChartEvent e) {
     if (_tooltipRoot == null) return;
     _tooltipRoot.style('opacity', '0');
   }
 }