Add mirrors tests

test/codegen/lib/mirrors/generics_helper.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.
+
+library generics_helper;
+
+import 'package:expect/expect.dart';
+
+typeParameters(mirror, parameterNames) {
+  Expect.listEquals(parameterNames,
+                    mirror.typeVariables.map((v) => v.simpleName).toList());
+}
+
+typeArguments(mirror, argumentMirrors) {
+  Expect.listEquals(argumentMirrors, mirror.typeArguments);
+}