Use "package:" imports for pub.

test/list_package_dirs/no_lockfile_test.dart

Index: test/list_package_dirs/no_lockfile_test.dart
diff --git a/test/list_package_dirs/no_lockfile_test.dart b/test/list_package_dirs/no_lockfile_test.dart
index 397e4a2b883dbb77a81581b0e130598cc88e63e6..1b3b55deaca3da32401d3b15df36dfa13fac0bc1 100644
--- a/test/list_package_dirs/no_lockfile_test.dart
+++ b/test/list_package_dirs/no_lockfile_test.dart
@@ -2,7 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE d.file.
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
+import 'package:pub/src/exit_codes.dart' as exit_codes;
+
 import '../descriptor.dart' as d;
 import '../test_pub.dart';