Add mirrors tests

test/codegen/lib/mirrors/reflect_uninstantiated_class_test.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.
+
+// A simple test that ensure that reflection works on uninstantiated classes.
+
+import "dart:mirrors";
+
+class Foo {
+  int a;
+}
+
+main() {
+  // Do NOT instantiate Foo.
+  var m = reflectClass(Foo);
+  var field = publicFields(m).single;
+  if (MirrorSystem.getName(field.simpleName) != 'a') {
+    throw 'Expected "a", but got "${MirrorSystem.getName(field.simpleName)}"';
+  }
+  print(field);
+}
+
+publicFields(ClassMirror mirror) =>
+    mirror.declarations.values.where(
+        (x) => x is VariableMirror && !(x.isPrivate || x.isStatic));