Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/test/install/git/check_out_twice_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 '../../descriptor.dart' as d;
 import '../../test_pub.dart';
@@ skipping 25 matching lines @@
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
 
     // Verify that nothing breaks if we install a Git revision that's already
     // in the cache.
     schedulePub(args: ['update'],
         output: new RegExp(r"Dependencies updated!$"));
   });
 }