Fix warnings_checker.dart handling of multitests

tests/lib_strong/mirrors/metadata_nested_constructor_call_test.dart

 // compile options: --emit-metadata
 // 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.
 
 // Regression test for Issue 17141.
 
 library test.metadata_nested_constructor_call;
 
 import 'dart:mirrors';
@@ skipping 11 matching lines @@
 
 @Box()
 class A {}
 
 @Box(const Box())
 class B {}
 
 @Box(const Box(const Box()))
 class C {}
 
-@Box(const Box(const MutableBox())) // /// 01: compile-time error
+@Box(const Box(const MutableBox())) // //# 01: compile-time error
 class D {}
 
-@Box(const MutableBox(const Box())) // /// 02: compile-time error
+@Box(const MutableBox(const Box())) // //# 02: compile-time error
 class E {}
 
-@Box(Box()) // /// 03: compile-time error
+@Box(Box()) // //# 03: compile-time error
 class F {}
 
-@Box(Box(const Box())) // /// 04: compile-time error
+@Box(Box(const Box())) // //# 04: compile-time error
 class G {}
 
-@Box(Box(const MutableBox())) // /// 05: compile-time error
+@Box(Box(const MutableBox())) // //# 05: compile-time error
 class H {}
 
-@Box(MutableBox(const Box())) // /// 06: compile-time error
+@Box(MutableBox(const Box())) // //# 06: compile-time error
 class I {}
 
 final closure = () => 42;
-@Box(closure()) // /// 07: compile-time error
+@Box(closure()) // //# 07: compile-time error
 class J {}
 
-@Box(closure) // /// 08: compile-time error
+@Box(closure) // //# 08: compile-time error
 class K {}
 
 function() => 42;
-@Box(function()) // /// 09: compile-time error
+@Box(function()) // //# 09: compile-time error
 class L {}
 
 // N.B. This is legal, but @function is not (tested by metadata_allowed_values).
 @Box(function)
 class M {}
 
 checkMetadata(DeclarationMirror mirror, List expectedMetadata) {
   Expect.listEquals(expectedMetadata.map(reflect).toList(), mirror.metadata);
 }
 
 main() {
   closure();
   checkMetadata(reflectClass(A), [const Box()]);
   checkMetadata(reflectClass(B), [const Box(const Box())]);
   checkMetadata(reflectClass(C), [const Box(const Box(const Box()))]);
   reflectClass(D).metadata;
   reflectClass(E).metadata;
   reflectClass(F).metadata;
   reflectClass(G).metadata;
   reflectClass(H).metadata;
   reflectClass(I).metadata;
   reflectClass(J).metadata;
   reflectClass(K).metadata;
   reflectClass(L).metadata;
   reflectClass(M).metadata;
 }