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

tests/standalone/io/path_test.dart

Index: tests/standalone/io/path_test.dart
diff --git a/tests/standalone/io/path_test.dart b/tests/standalone/io/path_test.dart
index 895295745e997b94c0c078da7afe8ef752ee0c3e..99756cb3d7de40592378a2a37b26b7dd7dd16bd3 100644
--- a/tests/standalone/io/path_test.dart
+++ b/tests/standalone/io/path_test.dart
@@ -9,6 +9,7 @@ import "dart:io";
 void main() {
   testBaseFunctions();
   testRaw();
+  testToNativePath();
   testCanonicalize();
   testJoinAppend();
   testRelativeTo();
@@ -115,6 +116,12 @@ void testRaw() {
   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());