Roll Observatory packages and add a roll script

packages/charted/lib/selection/selection_scope.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.selection;
 
@@ skipping 76 matching lines @@
    * Appends a new element to [root] and creates a selection containing
    * the newly added element.
    */
   Selection append(String tag) {
     var element = Namespace.createChildElement(tag, _root);
     root.children.add(element);
 
     return selectElements([element]);
   }
 }