Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/code_transformers/src/delete_file.dart

Index: observatory_pub_packages/code_transformers/src/delete_file.dart
===================================================================
--- observatory_pub_packages/code_transformers/src/delete_file.dart	(revision 0)
+++ observatory_pub_packages/code_transformers/src/delete_file.dart	(working copy)
@@ -0,0 +1,23 @@
+// Copyright (c) 2014, 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.
+
+/// Transformer that deletes everything that it sees, but only in release mode.
+library code_transformers.src.delete_file;
+
+import 'dart:async';
+import 'package:barback/barback.dart';
+
+// Deletes all files supplied in release mode.
+class DeleteFile extends Transformer {
+  BarbackSettings settings;
+
+  DeleteFile.asPlugin(this.settings);
+
+  /// Only apply to files in release mode.
+  isPrimary(_) => settings.mode == BarbackMode.RELEASE;
+
+  apply(Transform transform) {
+    transform.consumePrimary();
+  }
+}