Add a test for non-parameterized factory.

tests/language/src/NonParameterizedFactory2Test.dart

+// Copyright (c) 2011, 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.
+
+interface Interface<T> factory Factory {
+  Interface();
+  Interface.withArg(T value);
+}
+
+class Factory {
+  factory Interface<T>() {
+    return null;
+  }
+
+  factory Interface<T>.withArg(value) {
+    return null;
+  }
+}
+
+main() {
+  new Interface<int>();
+  new Interface<int>.withArg(4);
+}