Roll Observatory packages and add a roll script

packages/charted/lib/svg/shapes/arc.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.svg.shapes;
 
@@ skipping 111 matching lines @@
       ai = a.innerRadius,
       ao = a.outerRadius,
       bst = b.startAngle - ast,
       ben = b.endAngle - aen,
       bi = b.innerRadius - ai,
       bo = b.outerRadius - ao;
 
   return (t) => new SvgArcData(b.data, b.value,
     (ast + bst * t), (aen + ben * t), (ai + bi * t), (ao + bo * t));
 }