Fix warnings_checker.dart handling of multitests

tests/language/compile_time_constant_r_test.dart

Index: tests/language/compile_time_constant_r_test.dart
diff --git a/tests/language/compile_time_constant_r_test.dart b/tests/language/compile_time_constant_r_test.dart
index b186f7ea1441a36b2232956768e708fa00a64d9d..060c5bbf4cae422f18d2f14800036fd4f6b82622 100644
--- a/tests/language/compile_time_constant_r_test.dart
+++ b/tests/language/compile_time_constant_r_test.dart
@@ -3,18 +3,18 @@
 // BSD-style license that can be found in the LICENSE file.
 
 const x =
-          throw // /// 01: compile-time error
+          throw // //# 01: compile-time error
           "x";
 
 const y = const {0:
-                    throw // /// 02: compile-time error
+                    throw // //# 02: compile-time error
                     "y"};
 
 main() {
   print(x);
   print(y);
   const z =
-            throw // /// 03: compile-time error
+            throw // //# 03: compile-time error
             1+1+1;
   print(z);
 }