Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/update/pub_update_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 pub_tests;
 
 import 'dart:io';
 
 import 'package:scheduled_test/scheduled_test.dart';
 
@@ skipping 67 matching lines @@
     d.dir(appPath, [
       d.pubspec({"name": "myapp", "dependencies": {"foo": {"path": "../foo"}}})
     ]).create();
 
     schedulePub(args: ['update'],
         output: new RegExp(r"Dependencies updated!$"));
 
     d.packagesDir({"foo": null}).validate();
   });
 }