Use "package:" imports for pub.

test/list_package_dirs/lockfile_error_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 'package:path/path.dart' as path;
+import 'package:pub/src/exit_codes.dart' as exit_codes;
+import 'package:pub/src/io.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
-import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   integration("reports the lockfile path when there is an error in it", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.file("pubspec.lock", "some bad yaml")
     ]).create();
 
     schedulePub(args: ["list-package-dirs", "--format=json"],
         outputJson: {
           "error": contains('The lockfile must be a YAML mapping.'),
           "path": canonicalize(path.join(sandboxDir, appPath, "pubspec.lock"))
         },
         exitCode: exit_codes.DATA);
   });
 }