Use "package:" imports for pub.

test/transformer/can_log_messages_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.
 
 library pub_tests;
 
+import 'package:pub/src/exit_codes.dart' as exit_codes;
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/scheduled_stream.dart';
 
-import '../../lib/src/exit_codes.dart' as exit_codes;
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const SOURCE_MAPS_TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 import 'package:source_maps/source_maps.dart';
 
 class RewriteTransformer extends Transformer {
@@ skipping 94 matching lines @@
 
     // In barback >=0.15.0, the span will point to the location where the error
     // occurred.
     pub.stderr.expect(allow(inOrder(["d", "^"])));
 
     pub.stderr.expect("Build failed.");
 
     pub.shouldExit(exit_codes.DATA);
   });
 }