Allow private selectors to be typed, and fix ClassElement.isSubclassOf to take patches into account.

tests/language/private_selector_lib.dart

Index: tests/language/private_selector_lib.dart
===================================================================
--- tests/language/private_selector_lib.dart	(revision 0)
+++ tests/language/private_selector_lib.dart	(revision 0)
@@ -0,0 +1,19 @@
+// 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.
+
+library private_selector_lib;
+
+import 'private_selector_test.dart';
+
+bool executed = false;
+
+class A {
+  public() {
+    new B()._private();
+  }
+
+  _private() {
+    executed = true;
+  }
+}