Remove unnecessary coupling between Promise tests and Object.observe

test/mjsunit/es6/debug-promises/events.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --allow-natives-syntax --expose-debug-as debug
 
 Debug = debug.Debug;
 
 var eventsExpected = 16;
 var exception = null;
@@ skipping 98 matching lines @@
       assertAsync(exception === null, "exception === null");
       Debug.setListener(null);
     } else if (iteration > 10) {
       %AbortJS("Not all events were received!");
     } else {
       testDone(iteration + 1);
     }
   }
 
   var iteration = iteration || 0;
-  var dummy = {};
-  Object.observe(dummy, checkResult);
-  dummy.dummy = dummy;
+  %EnqueueMicrotask(checkResult);
 }
 
 testDone();