Use "package:" imports for pub.

test/build/outputs_error_to_json_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.
 
 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';
 
 const TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 class RewriteTransformer extends Transformer {
   RewriteTransformer.asPlugin();
@@ skipping 35 matching lines @@
                 "error": startsWith("Transform Rewrite on myapp|web/foo.txt "
                     "threw error: oh no!")
               }
             ],
             "log": []
           },
           exitCode: exit_codes.DATA);
     });
   });
 }