Fix warnings_checker.dart handling of multitests

tests/language/error_stacktrace_test.dart

Index: tests/language/error_stacktrace_test.dart
diff --git a/tests/language/error_stacktrace_test.dart b/tests/language/error_stacktrace_test.dart
index 90eb3f3af3362c98495a14b75cd574566637811b..9cb7f5a6130612b511b6c52ce4d7e18d5340b789 100644
--- a/tests/language/error_stacktrace_test.dart
+++ b/tests/language/error_stacktrace_test.dart
@@ -85,7 +85,7 @@ class Helper3 {
       try {
         // There should be no stackTrace in this normal exception object.
         // We should get a NoSuchMethodError.
-        var trace = e.stackTrace; /// static type warning
+        var trace = e.stackTrace; //# static type warning
       } on NoSuchMethodError catch (e) {
         Expect.isNotNull(e.stackTrace, "Error needs a stackTrace on throw");
       }