Roll Observatory packages and add a roll script

packages/barback/lib/src/transformer/transformer_group.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library barback.transformer.transformer_group;
 
 /// A [TransformerGroup] encapsulates a phased collection of transformers.
 ///
 /// A transformer group is defined like a collection of phases, such as you
 /// might pass to [Barback.updateTransformers]. Input assets are transformed by
@@ skipping 10 matching lines @@
   ///
   /// Each element of the inner iterable must be either a [Transformer] or a
   /// [TransformerGroup].
   final Iterable<Iterable> phases;
 
   TransformerGroup(Iterable<Iterable> phases)
       : this.phases = phases.map((phase) => phase.toList()).toList();
 
   String toString() => "group of $phases";
 }