Use "package:" imports for pub.

test/barback/fails_on_overlapping_directories_test.dart

 // Copyright (c) 2014, 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.
 
 import 'package:path/path.dart' as path;
+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(),
@@ skipping 24 matching lines @@
       args: [webSub1, webSub1Sub2],
       error: 'Directories "$webSub1" and "$webSub1Sub2" cannot overlap.',
       exitCode: exit_codes.USAGE);
 
   pubBuildAndServeShouldFail("if multiple directories overlap",
       args: [webSub1, webSub1Sub2, webSub1Sub3],
       error: 'Directories "$webSub1", "$webSub1Sub2" and "$webSub1Sub3" '
              'cannot overlap.',
       exitCode: exit_codes.USAGE);
 }