Roll Observatory packages and add a roll script

packages/charted/lib/selection/src/selection_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.selection;
 
 /**
@@ skipping 522 matching lines @@
   final DataSelection update;
   _ExitSelectionImpl(Iterable groups, DataSelection update)
       : update = update, super.selectionGroups(groups, update.scope);
 }
 
 class _SelectionGroupImpl implements SelectionGroup {
   Iterable<Element> elements;
   Element parent;
   _SelectionGroupImpl(this.elements, {this.parent});
 }