Remove unnecessary coupling between Promise tests and Object.observe

test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js

Index: test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js
diff --git a/test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js b/test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js
index 1ea1c7f9ff3eedb0318e9975c86b369ed734fd03..bd39a155ccb60099178e6ea755a68deb4af0304b 100644
--- a/test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js
+++ b/test/mjsunit/es6/debug-promises/throw-with-throw-in-reject.js
@@ -81,10 +81,7 @@ function testDone(iteration) {
     }
   }
 
-  // Run testDone through the Object.observe processing loop.
-  var dummy = {};
-  Object.observe(dummy, checkResult);
-  dummy.dummy = dummy;
+  %EnqueueMicrotask(checkResult);
 }
 
 testDone(0);