Fix warnings_checker.dart handling of multitests

tests/lib_strong/html/custom/element_upgrade_test.dart

Index: tests/lib_strong/html/custom/element_upgrade_test.dart
diff --git a/tests/lib_strong/html/custom/element_upgrade_test.dart b/tests/lib_strong/html/custom/element_upgrade_test.dart
index 6fd9def1c194ca5f2b6d2251a83f13d73ea9f9f1..07b8194e58b992272a2ff7a48b024c96999920e1 100644
--- a/tests/lib_strong/html/custom/element_upgrade_test.dart
+++ b/tests/lib_strong/html/custom/element_upgrade_test.dart
@@ -71,7 +71,7 @@ main() {
 
   test('cannot upgrade interfaces', () {
     expect(() {
-      upgrader.upgrade(new HtmlElementInterface()); /// compile-time error
+      upgrader.upgrade(new HtmlElementInterface()); //# compile-time error
     }, throws);
   });
 
@@ -115,7 +115,7 @@ main() {
   });
 }
 
-class HtmlElementInterface implements HtmlElement { /// compile-time error
+class HtmlElementInterface implements HtmlElement { //# compile-time error
   HtmlElementInterface.created();
 }