Add mirrors tests

test/codegen/lib/mirrors/deferred_mirrors_metadata_test.dart

+// 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.
+
+@A(const B())
+library main;
+
+@B()
+import 'package:async_helper/async_helper.dart';
+import 'package:expect/expect.dart';
+
+import "dart:math";
+
+import 'deferred_mirrors_metadata_lib.dart' deferred as lib1;
+
+class A {
+  final B b;
+  const A(this.b);
+  String toString() => "A";
+}
+
+class B {
+  const B();
+  String toString() => "B";
+}
+
+class C {
+  const C();
+  String toString() => "C";
+}
+
+class D {
+  const D();
+  String toString() => "D";
+}
+
+void main() {
+  asyncStart();
+  lib1.loadLibrary().then((_) {
+    Expect.equals("ABCD", lib1.foo());
+    new C();
+    new D();
+    asyncEnd();
+  });
+}