Use "package:" imports for pub.

test/list_package_dirs/no_lockfile_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 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';
 
 main() {
   initConfig();
   integration('with no lockfile, exits with error', () {
     d.dir(appPath, [
       d.appPubspec()
     ]).create();
 
     schedulePub(args: ["list-package-dirs", "--format=json"],
         outputJson: {
           "error":
             'Package "myapp" has no lockfile. Please run "pub get" first.'
         },
         exitCode: exit_codes.DATA);
   });
 }