Add argument check to Directory and Link constructors

tests/standalone/io/directory_invalid_arguments_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.
 
 import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 
 void testFailingList(Directory d, var recursive) {
   var port = new ReceivePort();
   int errors = 0;
   d.list(recursive: recursive).listen(
     () => Expect.fail("Unexpected listing result"),
     onError: (error) {
       errors += 1;
     },
     onDone: () {
       port.close();
       Expect.equals(1, errors);
     });
   Expect.equals(0, errors);
 }
 
 void testInvalidArguments() {
-  Directory d = new Directory(12);
   try {
-    d.existsSync();
+    Directory d = new Directory(12);
     Expect.fail("No exception thrown");
   } catch (e) {
     Expect.isTrue(e is ArgumentError);
   }
-  try {
-    d.deleteSync();
-    Expect.fail("No exception thrown");
-  } catch (e) {
-    Expect.isTrue(e is ArgumentError);
-  }
-  try {
-    d.createSync();
-    Expect.fail("No exception thrown");
-  } catch (e) {
-    Expect.isTrue(e is ArgumentError);
-  }
-  testFailingList(d, false);
-  Expect.throws(() => d.listSync(recursive: true),
-                (e) => e is ArgumentError);
-  d = new Directory(".");
+  Directory d = new Directory(".");
   testFailingList(d, 1);
   Expect.throws(() => d.listSync(recursive: 1),
                 (e) => e is ArgumentError);
 }
 
 main() {
   testInvalidArguments();
 }