Fix accessing private members on extension classes.

test/codegen/lib/html/private_extension_member_test.dart

Index: test/codegen/lib/html/private_extension_member_test.dart
diff --git a/test/codegen/lib/html/private_extension_member_test.dart b/test/codegen/lib/html/private_extension_member_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4512d9edf33a7d72d4cb6e8fabaee2b24f3c1b0c
--- /dev/null
+++ b/test/codegen/lib/html/private_extension_member_test.dart
@@ -0,0 +1,18 @@
+// Copyright (c) 2016, 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.
+
+import 'package:expect/expect.dart';
+
+import 'dart:html';
+
+main() {
+  // Regression test for: https://github.com/dart-lang/dev_compiler/issues/508.
+  // "dart:html" defines some private members on native DOM types and we need
+  // to ensure those can be accessed correctly.
+  //
+  // The createFragment() method sets `_innerHtml` on the element, so we use it
+  // as a test case.
+  Expect.equals("[object DocumentFragment]",
+      new BRElement().createFragment("Hi").toString());
+}