Get binstubs working on Windows.

sdk/lib/_internal/pub/test/global/binstubs/utils.dart

Index: sdk/lib/_internal/pub/test/global/binstubs/utils.dart
diff --git a/sdk/lib/_internal/pub/test/global/binstubs/utils.dart b/sdk/lib/_internal/pub/test/global/binstubs/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e52a1ebdfcd0798cb3595d6317ae0aba7930ccaf
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/global/binstubs/utils.dart
@@ -0,0 +1,13 @@
+// Copyright (c) 2014, 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';
+
+/// Returns the name of the shell script for a binstub named [name].
+///
+/// Adds a ".bat" extension on Windows.
+binStubName(String name) {
+  if (Platform.operatingSystem == "windows") return "$name.bat";
+  return name;
+}