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

tests/compiler/dart2js/patch_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.
 
 import "../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart";
 import "../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart";
 import "../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart";
 import "../../../sdk/lib/_internal/compiler/implementation/util/util.dart";
 import "mock_compiler.dart";
 import "parser_helper.dart";
@@ skipping 398 matching lines @@
                 "Unexpected warnings: ${compiler.warnings}");
   print('testExternalWithoutImplementationMember:${compiler.errors}');
   Expect.equals(1, compiler.errors.length);
   Expect.isTrue(
       compiler.errors[0].message.kind ==
           MessageKind.EXTERNAL_WITHOUT_IMPLEMENTATION);
   Expect.equals('External method without an implementation.',
                 compiler.errors[0].message.toString());
 }
 
+testIsSubclass() {
+  var compiler = applyPatch(
+      """
+      class A {}
+      """,
+      """
+      patch class A {}
+      """);
+  ClassElement cls = ensure(compiler, "A", compiler.coreLibrary.find,
+                            expectIsPatched: true);
+  ClassElement patch = cls.patch;
+  Expect.isTrue(cls != patch);
+  Expect.isTrue(cls.isSubclassOf(patch));
+  Expect.isTrue(patch.isSubclassOf(cls));
+}
+
 main() {
   testPatchFunction();
   testPatchMember();
   testPatchGetter();
   testRegularMember();
   testGhostMember();
   testInjectFunction();
   testPatchSignatureCheck();
 
   testExternalWithoutImplementationTopLevel();
   testExternalWithoutImplementationMember();
+
+  testIsSubclass();
 }