Use "package:" imports for pub.

test/dart2js/does_not_support_invalid_option_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 file.
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
+import 'package:pub/src/exit_codes.dart' as exit_codes;
+
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import '../serve/utils.dart';
 
 main() {
   initConfig();
   integration("doesn't support an invalid dart2js option", () {
     d.dir(appPath, [
       d.pubspec({
         "name": "myapp",
         "transformers": [{
           "\$dart2js": {"invalidOption": true}
         }]
       })
     ]).create();
 
     // TODO(nweiz): This should provide more context about how the option got
     // passed to dart2js. See issue 16008.
     var pub = startPubServe();
     pub.stderr.expect('Unrecognized dart2js option "invalidOption".');
     pub.shouldExit(exit_codes.DATA);
   });
 }