Fix warnings_checker.dart handling of multitests

tests/language/override_inheritance_mixed_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.
 
 class A {
-  var member1; /// 01: compile-time error
-  member2() {} /// 02: compile-time error
-  get member3 => null; /// 03: compile-time error
-  member4() {} /// 04: compile-time error
+  var member1; //# 01: compile-time error
+  member2() {} //# 02: compile-time error
+  get member3 => null; //# 03: compile-time error
+  member4() {} //# 04: compile-time error
 }
 
 abstract class I {
-  var member5; /// 05: ok
-  var member6; /// 06: static type warning
-  get member7; /// 07: static type warning
-  get member8; /// 08: static type warning
-  get member9; /// 09: static type warning
+  var member5; //# 05: ok
+  var member6; //# 06: static type warning
+  get member7; //# 07: static type warning
+  get member8; //# 08: static type warning
+  get member9; //# 09: static type warning
 }
 
 abstract class J {
-  get member5; /// 05: continued
-  member6() {} /// 06: continued
-  member7() {} /// 07: continued
-  member8() {} /// 08: continued
-  member9() {} /// 09: continued
+  get member5; //# 05: continued
+  member6() {} //# 06: continued
+  member7() {} //# 07: continued
+  member8() {} //# 08: continued
+  member9() {} //# 09: continued
 }
 
 abstract class B extends A implements I, J {
 }
 
 class Class extends B {
-  member1() {} /// 01: continued
-  var member2; /// 02: continued
-  member3() {} /// 03: continued
-  get member4 => null; /// 04: continued
-  var member5; /// 05: continued
-  member8() {} /// 08: continued
-  get member9 => null; /// 09: continued
+  member1() {} //# 01: continued
+  var member2; //# 02: continued
+  member3() {} //# 03: continued
+  get member4 => null; //# 04: continued
+  var member5; //# 05: continued
+  member8() {} //# 08: continued
+  get member9 => null; //# 09: continued
 }
 
 main() {
   new Class();
 }