Use "package:" imports for pub.

test/barback/fails_if_dir_arg_does_not_exist_test.dart

 // Copyright (c) 2014, 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 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';
 
 main() {
   initConfig();
 
   setUp(() {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("bar", [
         d.file("file.txt", "contents")
       ])
     ]).create();
   });
 
   pubBuildAndServeShouldFail("if a specified directory doesn't exist",
       args: ["foo", "bar", "baz"],
       error: 'Directories "foo" and "baz" do not exist.',
       exitCode: exit_codes.DATA);
 }