Adds limited support for private classes.

test_reflectable/test/private_class_library.dart

+// Copyright (c) 2015, the Dart Team. All rights reserved. Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+/// File being transformed by the reflectable transformer.
+/// Part of the entry point 'private_class_test.dart'.
+library test_reflectable.test.private_class_library;
+
+class PublicClass {
+  int publicMethod() => 42;
+}
+
+class _PrivateClass1 extends PublicClass {
+  int supposedlyPrivate() => -42;
+}
+
+class PublicSubclass1 extends _PrivateClass1 {}
+
+class _PrivateClass2 implements PublicClass {
+  int publicMethod() => 43;
+  int supposedlyPrivateToo() => -43;
+}
+
+class PublicSubclass2 extends _PrivateClass2 {}
+
+PublicClass func1() => new _PrivateClass1();
+
+PublicClass func2() => new _PrivateClass2();
+
+PublicClass func3() => new PublicSubclass1();
+
+PublicClass func4() => new PublicSubclass2();