Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/barback.dart

Index: observatory_pub_packages/barback/barback.dart
===================================================================
--- observatory_pub_packages/barback/barback.dart	(revision 0)
+++ observatory_pub_packages/barback/barback.dart	(working copy)
@@ -0,0 +1,28 @@
+// 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;
+
+export 'src/asset/asset.dart';
+export 'src/asset/asset_id.dart';
+export 'src/asset/asset_set.dart';
+export 'src/barback.dart';
+export 'src/build_result.dart';
+export 'src/errors.dart' hide flattenAggregateExceptions;
+export 'src/log.dart';
+export 'src/package_provider.dart';
+export 'src/transformer/aggregate_transform.dart';
+export 'src/transformer/aggregate_transformer.dart';
+export 'src/transformer/barback_settings.dart';
+export 'src/transformer/base_transform.dart';
+export 'src/transformer/declaring_aggregate_transform.dart';
+export 'src/transformer/declaring_aggregate_transformer.dart';
+export 'src/transformer/declaring_transform.dart' hide newDeclaringTransform;
+export 'src/transformer/declaring_transformer.dart';
+export 'src/transformer/lazy_aggregate_transformer.dart';
+export 'src/transformer/lazy_transformer.dart';
+export 'src/transformer/transform.dart' hide newTransform;
+export 'src/transformer/transform_logger.dart';
+export 'src/transformer/transformer.dart';
+export 'src/transformer/transformer_group.dart';