Add mirrors tests

test/codegen/lib/mirrors/top_level_accessors_test.dart

+// Copyright (c) 2012, 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 test.top_level_accessors_test;
+
+import 'dart:mirrors';
+
+import 'package:expect/expect.dart';
+
+var field;
+
+get accessor => field;
+
+set accessor(value) {
+  field = value;
+  return 'fisk';
+}
+
+main() {
+  LibraryMirror library = currentMirrorSystem()
+      .findLibrary(#test.top_level_accessors_test);
+  field = 42;
+  Expect.equals(42, library.getField(#accessor).reflectee);
+  Expect.equals(87, library.setField(#accessor, 87).reflectee);
+  Expect.equals(87, field);
+  Expect.equals(87, library.getField(#accessor).reflectee);
+}