Fix flakiness of imported/web-platform-tests/html/syntax/parsing/html5lib_testsNN.html.

LayoutTests/imported/web-platform-tests/resources/testharnessreport.js

 /*
  * THIS FILE INTENTIONALLY LEFT BLANK
  *
  * More specifically, this file is intended for vendors to implement
  * code needed to integrate testharness.js tests with their own test systems.
  *
  * Typically such integration will attach callbacks when each test is
  * has run, using add_result_callback(callback(test)), or when the whole test file has
  * completed, using add_completion_callback(callback(tests, harness_status)).
  *
@@ skipping 108 matching lines @@
             document.documentElement.appendChild(document.createElement("body"));
         document.body.appendChild(results);
 
         if (self.testRunner)
             testRunner.notifyDone();
     }
 
     if (document.readyState === 'loading') {
         window.addEventListener('load', done);
     } else {
-        done();
+        setTimeout(done, 0);
     }
 });