Use "package:" imports for pub.

test/pub_get_and_upgrade_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS 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.
 
 library pub_tests;
 
+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';
 
 main() {
   initConfig();
 
   forBothPubGetAndUpgrade((command) {
     group('requires', () {
       integration('a pubspec', () {
         d.dir(appPath, []).create();
@@ skipping 116 matching lines @@
           }
         })
       ]).create();
 
       pubCommand(command,
           error: contains('A package may not list itself as a dependency.'),
           exitCode: exit_codes.DATA);
     });
   });
 }