ignore `@proxy` in strong mode

tests/language_strong/deferred_no_such_method_test.dart

 // Copyright (c) 2014, 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 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 
 import "deferred_no_such_method_lib.dart" deferred as lib;
 
 void main() {
   asyncStart();
   lib.loadLibrary().then((_) {
-    Expect.equals(42, new lib.C().nonExisting());
+    Expect.equals(42, (new lib.C() as dynamic).nonExisting());
     asyncEnd();
   });
 }