Fix warnings_checker.dart handling of multitests

tests/language_strong/setter_override_test.dart

 // Copyright (c) 2013, 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 we do not report a compile-time error when a static setter named
 // foo= is declared in a class inheriting an instance method or getter named
 // foo, and that we do report an error if an instance setter named foo= or
 // instance field name foo is inherited.
 
 import "package:expect/expect.dart";
 
 class A {
-  var foo = 42; // /// 00: compile-time error
-  get foo => 42; // /// 01: static type warning
-  foo() => 42; // /// 02: static type warning
-  set foo(value) { } // /// 03: compile-time error
+  var foo = 42; // //# 00: compile-time error
+  get foo => 42; // //# 01: static type warning
+  foo() => 42; // //# 02: static type warning
+  set foo(value) { } // //# 03: compile-time error
 }
 
 class B extends A {
   static var foo_;
   static set foo(value) { foo_ = value; }
 }
 
 main() {
   B.foo = 42;
   Expect.equals(42, B.foo_);
 }