Make Zone API strong mode clean.

tests/lib/async/zone_debug_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'dart:async';
 
 import 'dart:collection';
 
@@ skipping 98 matching lines @@
       Expect.listEquals([fork2Trace, globalTrace], restoredStackTrace);
       fork3Trace = stackTrace;
       openTests--;
       if (openTests == 0) {
         done.complete();
       }
       scheduleMicrotask(() {
         expectedDebugTrace = [fork3Trace, fork2Trace, globalTrace];
         throw "gee";
       });
-    }, runGuarded: false);
-  }, runGuarded: false);
+    });
+  });
   openTests++;
   f();
   f2();
 
   done.future.whenComplete(() {
     // We don't really care for the order.
     events.sort();
     Expect.listEquals([
       "handling uncaught error bar",
       "handling uncaught error foo",
       "handling uncaught error gee"
     ], events);
     asyncEnd();
   });
 }