Use "package:" imports for pub.

test/get/path/empty_pubspec_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 p;
+import 'package:pub/src/exit_codes.dart' as exit_codes;
 
-import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   // Regression test for issue 20103.
   integration('path dependency to an empty pubspec', () {
     d.dir('foo', [
       d.libDir('foo'),
       d.file('pubspec.yaml', '')
     ]).create();
 
     d.dir(appPath, [
       d.appPubspec({
         "foo": {"path": "../foo"}
       })
     ]).create();
 
     pubGet(exitCode: exit_codes.DATA, error:
         'Error on line 1, column 1 of ${p.join('..', 'foo', 'pubspec.yaml')}: '
             'Missing the required "name" field.');
   });
 }