Roll Observatory packages and add a roll script

packages/charted/lib/charts/chart_state.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 130 matching lines @@
 }
 
 ///
 /// Implementation of [ChangeRecord], that is used to notify changes to
 /// values in [ChartData].
 ///
 class ChartPreviewChangeRecord implements ChangeRecord {
   final int previewed;
   const ChartPreviewChangeRecord(this.previewed);
 }