Fix warnings_checker.dart handling of multitests

tests/language_strong/super_call3_test.dart

Index: tests/language_strong/super_call3_test.dart
diff --git a/tests/language_strong/super_call3_test.dart b/tests/language_strong/super_call3_test.dart
index a477cfa15b769990e17a3edc577d08bdd18e4965..56762fc0ea0c08babb8e9dc67ccb89827e88b046 100644
--- a/tests/language_strong/super_call3_test.dart
+++ b/tests/language_strong/super_call3_test.dart
@@ -8,7 +8,7 @@ import "package:expect/expect.dart";
 
 class A {
   A(
-    this.x // /// 01: compile-time error
+    this.x // //# 01: compile-time error
   );
   final foo = 499;
 }
@@ -23,7 +23,7 @@ class B2 extends A {
 
 class C {
   C
-  .named // /// 02: compile-time error
+  .named // //# 02: compile-time error
   ();
   final foo = 499;
 }