Allow paths up to 32767 characters on Windows (so '\\?\' can be used).

tests/standalone/io/file_windows_test.dart

+// Copyright (c) 2013, 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 'dart:io';
+
+import "package:expect/expect.dart";
+
+void testDeleteLongPathPrefix() {
+  var dir = Directory.systemTemp.createTempSync('dart_file_win');
+  var dirPath = "\\\\?\\${dir.path}";
+  var subPath = dirPath;
+  for (int i = 0; i < 16; i++) {
+    subPath += "\\a-long-path-segment";
+    dir = new Directory(subPath)..createSync();
+  }
+  Expect.isTrue(dir.path.length > 256);
+  var prefixDir = new Directory(dirPath);
+  Expect.isTrue(prefixDir.existsSync());
+  prefixDir.deleteSync(recursive: true);
+  Expect.isFalse(dir.existsSync());
+  Expect.isFalse(prefixDir.existsSync());
+}
+
+
+void main() {
+  if (!Platform.isWindows) return;
+  testDeleteLongPathPrefix();
+}