Add builtin detector to generate-runtime-tests.py

src/v8natives.js

 // Copyright 2012 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.
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Boolean = global.Boolean;
 // var $Number = global.Number;
 // var $Function = global.Function;
@@ skipping 1868 matching lines @@
     var microtasks = microtaskState.queue;
     microtaskState.queue = null;
 
     for (var i = 0; i < microtasks.length; i++) {
       microtasks[i]();
     }
   }
 }
 
 function EnqueueMicrotask(fn) {
+  if (!IS_FUNCTION(func)) {
+    throw new $TypeError('Can only enqueue functions');
+  }
   var microtaskState = %GetMicrotaskState();
   if (IS_UNDEFINED(microtaskState.queue) || IS_NULL(microtaskState.queue)) {
     microtaskState.queue = new InternalArray;
   }
   microtaskState.queue.push(fn);
   %SetMicrotaskPending(true);
 }