Make Zone API strong mode clean.

tests/lib_strong/mirrors/invocation_fuzz_test.dart

Index: tests/lib_strong/mirrors/invocation_fuzz_test.dart
diff --git a/tests/lib_strong/mirrors/invocation_fuzz_test.dart b/tests/lib_strong/mirrors/invocation_fuzz_test.dart
index 166d7288e28ff17b426a67fdd9aba48e647b315d..6fd37962832ccad59ee53c660b976eead0414967 100644
--- a/tests/lib_strong/mirrors/invocation_fuzz_test.dart
+++ b/tests/lib_strong/mirrors/invocation_fuzz_test.dart
@@ -190,8 +190,8 @@ main() {
   ];
   valueObjects.forEach((v) => checkInstance(reflect(v), 'value object'));
 
-  uncaughtErrorHandler(self, parent, zone, error, stack) {}
-  ;
+  void uncaughtErrorHandler(self, parent, zone, error, stack) {}
+
   var zoneSpec =
       new ZoneSpecification(handleUncaughtError: uncaughtErrorHandler);
   testZone = Zone.current.fork(specification: zoneSpec);