Roll Observatory packages and add a roll script

packages/charted/lib/charts/src/chart_axis_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 186 matching lines @@
 
       // Check if we have enough space to render full chart
       allowedWidth = (1.4142 * (rectHeight)) - (textMetrics.fontSize / 1.4142);
       if (maxLabelWidth > allowedWidth) {
         shortenedTicks = formattedTicks.map(
             (x) => textMetrics.ellipsizeText(x, allowedWidth)).toList();
       }
     }
   }
 }