Handle @proxy classes in type checker.

tests/compiler/dart2js/proxy_test.dart

Index: tests/compiler/dart2js/proxy_test.dart
diff --git a/tests/compiler/dart2js/least_upper_bound_language_test.dart b/tests/compiler/dart2js/proxy_test.dart
similarity index 73%
copy from tests/compiler/dart2js/least_upper_bound_language_test.dart
copy to tests/compiler/dart2js/proxy_test.dart
index f75c32c63f4af501991d1185ef62bdccde7e0beb..c558350c12097c8ffd881f91fbccdb6c5ca48645 100644
--- a/tests/compiler/dart2js/least_upper_bound_language_test.dart
+++ b/tests/compiler/dart2js/proxy_test.dart
@@ -2,9 +2,9 @@
 // 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.
 
-// Test that dart2js produces the expected static type warnings for least upper
-// bound language tests. This ensures that the analyzer and dart2js agrees
-// on these tests.
+// Test that dart2js produces the expected static type warnings for proxy
+// language tests. This ensures that the analyzer and dart2js agrees on these
+// tests.
 
 import 'warnings_checker.dart';
 
@@ -13,8 +13,8 @@ import 'warnings_checker.dart';
 /// can contain a list of line numbers for keys 'missing' and 'unexpected' for
 /// the warnings of each category.
 const Map<String, dynamic> TESTS = const {
-    'language/least_upper_bound_test.dart': null,
-    'language/least_upper_bound_expansive_test.dart': null,
+    'language/proxy_test.dart': null,
+    'language/proxy2_test.dart': null,
 };
 
 void main() {