Fix inconsistent arguments types in expectAsyncN methods.

tests/isolate/count_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.
 
 library CountTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import 'dart:isolate';
 
 void countMessages() {
   int count = 0;
@@ skipping 28 matching lines @@
         expect(count, 11);
         local.close();
         return;
       }
 
       expect(message, (count - 1) * 2);
       remote.send(count++, reply);
       if (count == 10) {
         remote.send(-1, reply);
       }
-    }, 11));
+    }, count: 11));
     remote.send(count++, reply);
   });
 }