Fix some bugs regarding native fields.

dart/tests/compiler/dart2js_native/rti_only_native_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.
+
+// Regression test for a bug that was caused by uninstantiated classes being
+// added to emitted classes by runtime-type system.
+// See my explanation in https://codereview.chromium.org/14018036/.
+//   -- ahe
+
+class A native "A" {
+  // Just making sure the field name is unique.
+  var rti_only_native_test_field;
+}
+
+typedef fisk();
+
+main() {
+  void foo(A x) {}
+  var map = { 'a': 0, 'b': main };
+  try {
+    map.values.forEach((x) => x.rti_only_native_test_field);
+  } finally {
+    print(main is fisk);
+    return;
+  }
+}