Roll Observatory packages and add a roll script

packages/charted/lib/charts/src/chart_events_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;
 
@@ skipping 27 matching lines @@
     var hostRect = area.host.getBoundingClientRect(),
         left = area.config.isRTL
             ? area.theme.padding.end
             : area.theme.padding.start;
     if (source != null) {
       chartX = source.client.x - hostRect.left - left;
       chartY = source.client.y - hostRect.top - area.theme.padding.top;
     }
   }
 }