Update charted to 0.4.8 and roll

packages/charted/lib/charts/src/chart_state_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;
 
 ///
 /// Model that maintains state of each visualization item. Each entry in the
 /// legend is considered one visualization item.
 /// - In [CartesianArea] it is always a column.
 /// - In [LayoutArea] renders choose either columns or rows.
 ///
-class DefaultChartStateImpl extends ChangeNotifier implements ChartState {
+class DefaultChartStateImpl extends Observable implements ChartState {
   final bool isMultiSelect;
   final bool isMultiHighlight;
   final bool isSelectOrHighlight;
   final bool supportColumnSelection;
   final bool supportColumnPreview;
   final bool supportValueHighlight;
   final bool supportValueHover;
 
   LinkedHashSet<int> hidden = new LinkedHashSet<int>();
 
@@ skipping 96 matching lines @@
       var item = new Pair<int, int>(column, row);
       highlights.remove(item);
       notifyChange(new ChartHighlightChangeRecord(remove: item));
     }
     return false;
   }
 
   bool isHighlighted(int column, int row) =>
       highlights.any((x) => x.first == column && x.last == row);
 }