Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/directory_tree_test.dart

 // Copyright (c) 2012, 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.
 
 library lock_file_test;
 
 import 'package:unittest/unittest.dart';
 
-import '../../pub/directory_tree.dart';
+import '../lib/src/directory_tree.dart';
 
 main() {
   test('no files', () {
     expect(generateTree([]), equals(""));
   });
 
   test('up to ten files in one directory are shown', () {
     var files = [
       "dir/a.dart",
       "dir/b.dart",
@@ skipping 117 matching lines @@
     |-- absolute_test.dart
     |-- all_test.dart
     |-- basename_test.dart
     | (7 more...)
     |-- path_windows_test.dart
     |-- relative_test.dart
     '-- split_test.dart
 """));
   });
 }