Get rid of join() and encapsulate File and Directory in io.dart.

utils/pub/validator/name.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 name_validator;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../../../pkg/path/lib/path.dart' as path;
@@ skipping 30 matching lines @@
         warnings.add('The name of "${libraries[0]}", "$libName", should match '
             'the name of the package, "${entrypoint.root.name}".\n'
             'This helps users know what library to import.');
       }
     });
   }
 
   /// Returns a list of all libraries in the current package as paths relative
   /// to the package's root directory.
   Future<List<String>> get _libraries {
-    var libDir = join(entrypoint.root.dir, "lib");
+    var libDir = path.join(entrypoint.root.dir, "lib");
     return defer(() {
       if (!dirExists(libDir)) return [];
       return listDir(libDir, recursive: true);
     }).then((files) {
       return files
           .map((file) => path.relative(file, from: path.dirname(libDir)))
           .where((file) => !path.split(file).contains("src") &&
                            path.extension(file) == '.dart')
           .toList();
     });
@@ skipping 25 matching lines @@
       builder
         ..add(source.substring(lastMatchEnd, match.start + 1))
         ..add("_")
         ..add(match.group(1).toLowerCase());
       lastMatchEnd = match.end;
     }
     builder.add(source.substring(lastMatchEnd));
     return builder.toString().toLowerCase();
   }
 }