dart:io | The empty path should return "." for its toNativePath value.

tests/standalone/io/path_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.
 //
 // Test the Path class in dart:io.
 
 import "dart:io";
 
 void main() {
   testBaseFunctions();
   testRaw();
+  testToNativePath();
   testCanonicalize();
   testJoinAppend();
   testRelativeTo();
   testWindowsShare();
   testWindowsDrive();
 }
 
 void testBaseFunctions() {
   testGetters(new Path("/foo/bar/fisk.hest"),
               ['/foo/bar', 'fisk.hest', 'fisk', 'hest'],
@@ skipping 86 matching lines @@
   Expect.equals(path.isAbsolute, properties.contains('absolute'));
   Expect.equals(path.hasTrailingSeparator, properties.contains('trailing'));
 }
 
 void testRaw() {
   Expect.equals(new Path.raw('c:\\foo/bar bad').toString(), 'c:\\foo/bar bad');
   Expect.equals(new Path.raw('').toString(), '');
   Expect.equals(new Path.raw('\\bar\u2603\n.').toString(), '\\bar\u2603\n.');
 }
 
+void testToNativePath() {
+  Expect.equals('.', new Path('').toNativePath());
+  Expect.equals('.', new Path('.').toNativePath());
+  Expect.equals('.', new Path('a_file').directoryPath.toNativePath());
+}
+
 void testCanonicalize() {
   Function t = (input, canonicalized) {
     Expect.equals(canonicalized, new Path(input).canonicalize().toString());
   };
 
   t('.', '.');
   t('./.', '.');
   t('foo/..', '.');
   t('../foo', '../foo');
   t('/../foo', '/foo');
@@ skipping 196 matching lines @@
   Expect.equals('../../c', CPath.relativeTo(cPath).toString());
   Expect.equals('../b/d', cPath.relativeTo(CPath).toString());
   Expect.equals('.', DPath.relativeTo(DPath).toString());
   Expect.equals('.', NoPath.relativeTo(NoPath).toString());
   Expect.equals('.', C2Path.relativeTo(cPath).toString());
   Expect.equals('..', C3Path.relativeTo(cPath).toString());
   Expect.equals('d', cPath.relativeTo(C3Path).toString());
   Expect.equals('a/b/d', cPath.relativeTo(C4Path).toString());
   Expect.equals('../../../', C4Path.relativeTo(cPath).toString());
 }