Remove unnecessary coupling between Promise tests and Object.observe

test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js

Index: test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js
diff --git a/test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js b/test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js
index 36b5565e5f807dcf5ef4e763167ce0d5155775d7..3c30ad3f7cbf3ee3096b4e7b7ef9fc54beca364f 100644
--- a/test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js
+++ b/test/mjsunit/es6/debug-promises/throw-caught-by-default-reject-handler.js
@@ -78,10 +78,7 @@ function testDone(iteration) {
     }
   }
 
-  // Run testDone through the Object.observe processing loop.
-  var dummy = {};
-  Object.observe(dummy, checkResult);
-  dummy.dummy = dummy;
+  %EnqueueMicrotask(checkResult);
 }
 
 testDone(0);