Add mirrors tests

test/codegen/lib/mirrors/optional_parameters_test.dart

+// Copyright (c) 2015, 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.
+
+// Regression test for http://dartbug.com/22987.
+// Ensure that functions whose signature only differs in optionality of
+// parameters are reflected correctly.
+
+library optional_parameter_test;
+
+@MirrorsUsed(targets: 'optional_parameter_test')
+import "dart:mirrors";
+import 'package:expect/expect.dart';
+
+class A {
+  foo(int x) => x;
+}
+
+class B {
+  foo([int x]) => x+1;
+}
+
+main () {
+  var x = {};
+  x["A"] = reflect(new A());
+  x["B"] = reflect(new B());
+
+  Expect.equals(1, x["A"].invoke(#foo, [1]).reflectee);
+  Expect.equals(2, x["B"].invoke(#foo, [1]).reflectee);
+}