Fix warnings_checker.dart handling of multitests

tests/language_strong/generic_methods_recursive_bound_test.dart

 // Copyright (c) 2017, 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.
 
 // Test that F-bounded quantification works for generic methods, and that types
 // that are passed to generic methods in dynamic calls are checked for being
 // recursively defined.
 
 library generic_methods_recursive_bound_test;
 
 import "package:expect/expect.dart";
 
 abstract class I<T> {
   bool fun(T x);
 }
 
 void foo<T extends I<T>>(List<T> a) {
   if (a.length > 1) {
     a[0].fun(a[1]);
   }
 }
 
 class C implements I<C> {
   bool fun(C c) => true;
 }
 
 main() {
-  foo<C>(<C>[new C(), new C()]); /// 01: ok
+  foo<C>(<C>[new C(), new C()]); //# 01: ok
 
   dynamic bar = foo;
   List<int> list2 = <int>[4, 2];
   // The type int does not extend I<int>.
-  foo<int>(list2); /// 02: compile-time error
-  bar<int>(list2); /// 03: runtime error
+  foo<int>(list2); //# 02: compile-time error
+  bar<int>(list2); //# 03: runtime error
 }