Use "package:" imports for pub.

test/barback/fails_if_dir_arg_does_not_exist_test.dart

Index: test/barback/fails_if_dir_arg_does_not_exist_test.dart
diff --git a/test/barback/fails_if_dir_arg_does_not_exist_test.dart b/test/barback/fails_if_dir_arg_does_not_exist_test.dart
index 2f5d56e9ac1427f4d7d620c90903c1bb625f42a9..92f9a362e6195a0d38fc3f90a5331c580b791b2e 100644
--- a/test/barback/fails_if_dir_arg_does_not_exist_test.dart
+++ b/test/barback/fails_if_dir_arg_does_not_exist_test.dart
@@ -2,9 +2,9 @@
 // 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.
 
+import 'package:pub/src/exit_codes.dart' as exit_codes;
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';