Compute correct constructor type for synthesized mixin constructors.

tests/compiler/dart2js/mixin_language_test.dart

Index: tests/compiler/dart2js/mixin_language_test.dart
diff --git a/tests/compiler/dart2js/proxy_test.dart b/tests/compiler/dart2js/mixin_language_test.dart
similarity index 80%
copy from tests/compiler/dart2js/proxy_test.dart
copy to tests/compiler/dart2js/mixin_language_test.dart
index c558350c12097c8ffd881f91fbccdb6c5ca48645..f4be3b2011702f84dc5e75b4b21949e5fe7df7e8 100644
--- a/tests/compiler/dart2js/proxy_test.dart
+++ b/tests/compiler/dart2js/mixin_language_test.dart
@@ -2,8 +2,8 @@
 // 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 proxy
-// language tests. This ensures that the analyzer and dart2js agrees on these
+// Test that dart2js produces the expected static type warnings for these
+// language tests. This ensures that the analyzer and dart2js agrees on the
 // tests.
 
 import 'warnings_checker.dart';
@@ -13,10 +13,9 @@ 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/proxy_test.dart': null,
-    'language/proxy2_test.dart': null,
+    'language/typevariable_substitution2_test.dart': null,
 };
 
-void main() {
-  checkWarnings(TESTS);
+void main(List<String> arguments) {
+  checkWarnings(TESTS, arguments);
 }