Fix warnings_checker.dart handling of multitests

tests/language/multiline_newline_test.dart

 // Copyright (c) 2015, 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.
 
 import 'package:expect/expect.dart';
 import 'multiline_newline_cr.dart' as cr;
 import 'multiline_newline_crlf.dart' as crlf;
 import 'multiline_newline_lf.dart' as lf;
 
 main() {
@@ skipping 14 matching lines @@
   const c1 =
       cr.constantMultilineString == crlf.constantMultilineString ? true : null;
   const c2 =
       crlf.constantMultilineString == lf.constantMultilineString ? true : null;
   const c3 =
       lf.constantMultilineString == cr.constantMultilineString ? true : null;
   Expect.isTrue(c1);
   Expect.isTrue(c2);
   Expect.isTrue(c3);
 
-  const c4 = c1 ? 1 : 2; // /// 01: ok
-  Expect.equals(1, c4); //  /// 01: continued
+  const c4 = c1 ? 1 : 2; // //# 01: ok
+  Expect.equals(1, c4); //  //# 01: continued
 
-  const c5 = c2 ? 2 : 3; // /// 02: ok
-  Expect.equals(2, c5); //  /// 02: continued
+  const c5 = c2 ? 2 : 3; // //# 02: ok
+  Expect.equals(2, c5); //  //# 02: continued
 
-  const c6 = c3 ? 3 : 4; // /// 03: ok
-  Expect.equals(3, c6); //  /// 03: continued
+  const c6 = c3 ? 3 : 4; // //# 03: ok
+  Expect.equals(3, c6); //  //# 03: continued
 
   const c7 =
       cr.constantMultilineString != crlf.constantMultilineString ? true : null;
   const c8 =
       crlf.constantMultilineString != lf.constantMultilineString ? true : null;
   const c9 =
       lf.constantMultilineString != cr.constantMultilineString ? true : null;
   Expect.isNull(c7);
   Expect.isNull(c8);
   Expect.isNull(c9);
 
-  const c10 = c7 ? 1 : 2; // /// 04: compile-time error
-  const c11 = c8 ? 2 : 3; // /// 05: compile-time error
-  const c12 = c9 ? 3 : 4; // /// 06: compile-time error
+  const c10 = c7 ? 1 : 2; // //# 04: compile-time error
+  const c11 = c8 ? 2 : 3; // //# 05: compile-time error
+  const c12 = c9 ? 3 : 4; // //# 06: compile-time error
 }