Use "package:" imports for pub.

test/serve/missing_file_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:path/path.dart' as path;
+import 'package:pub/src/io.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
-import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 main() {
   initConfig();
   integration("responds with a 404 for missing source files", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir("lib", [
@@ skipping 18 matching lines @@
     // TODO(rnystrom): It's possible for these requests to happen quickly
     // enough that the file system hasn't notified for the deletions yet. If
     // that happens, we can probably just add a short delay here.
 
     requestShould404("index.html");
     requestShould404("packages/myapp/nope.dart");
     requestShould404("dir/packages/myapp/nope.dart");
     endPubServe();
   });
 }