Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/lib/src/validator/directory.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 directory_validator;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
@@ skipping 28 matching lines @@
 
         if (dir.contains(new RegExp(r"^samples?$"))) {
           warnings.add('Rename the top-level "$dir" directory to "example".\n'
               'This allows Pub to find your examples and create "packages" '
                   'directories for them.\n');
         }
       }
     });
   }
 }