Roll Observatory packages and add a roll script

packages/charted/lib/charts/behaviors/axis_label_tooltip.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 100 matching lines @@
 
     if (y + tooltip.height > renderArea.bottom) {
       y = renderArea.bottom - tooltip.height;
     } else if (y < renderArea.top) {
       y = renderArea.top;
     }
 
     return new math.Point(x - _hostAreaRect.left, y - _hostAreaRect.top);
   }
 }