Roll Observatory packages and add a roll script

packages/charted/lib/charts/behaviors/line_marker.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 94 matching lines @@
 
     if (animate) {
       _markers.transition()
           .attrWithCallback('d', (d, i, e) => _getMarkerPath(d, false));
     }
 
     _markers.exit.remove();
   }
 }