Fix warnings_checker.dart handling of multitests

tests/language/final_initializer_instance_reference_test.dart

 // Copyright (c) 2016, 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.
 
 // Dart2js regression test. Error in initializer might be report with the wrong
 // current element.
 
 class C {
   const C();
 
   final x = 1;
-  final y = x; /// 01: compile-time error
+  final y = x; //# 01: compile-time error
 }
 
 main() {
-  const C().y; /// 01: continued
+  const C().y; //# 01: continued
 }