Fix warnings_checker.dart handling of multitests

tests/language/mixin_supertype_subclass3_test.dart

Index: tests/language/mixin_supertype_subclass3_test.dart
diff --git a/tests/language/mixin_supertype_subclass3_test.dart b/tests/language/mixin_supertype_subclass3_test.dart
index 7ca889d5d6968e9a39418de1d77c8d159e800f69..584e4443c0036d82110eb7e16487d28159276221 100644
--- a/tests/language/mixin_supertype_subclass3_test.dart
+++ b/tests/language/mixin_supertype_subclass3_test.dart
@@ -19,11 +19,11 @@ class D {}
 class E extends B with C implements D {}
 class F extends E {}
 class A
-  = E with M; class M = B with G; class G /// 01: ok
-  = E with M; class M = C with G; class G /// 02: static type warning
-  = E with M; class M = D with G; class G /// 03: ok
-  = E with M; class M = E with G; class G /// 04: ok
-  = E with M; class M = F with G; class G /// 05: static type warning
+  = E with M; class M = B with G; class G //# 01: ok
+  = E with M; class M = C with G; class G //# 02: static type warning
+  = E with M; class M = D with G; class G //# 03: ok
+  = E with M; class M = E with G; class G //# 04: ok
+  = E with M; class M = F with G; class G //# 05: static type warning
   {}
 
 main() {