Stable unexpected results (1): 
  ▶ ERROR [expected TIMEOUT] /performance-timeline/not-restored-reasons/abort-block-bfcache.window.html
  │   → window.__wptrunner_process_next_event is not a function
  │   → Traceback (most recent call last):
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 1186, in run_func
  │   →     self.result = True, self.func(self.protocol, self.url, self.timeout)
  │   →                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 1283, in do_testharness
  │   →     raw_results = protocol.testdriver.run(url, self.script_resume, test_window)
  │   →                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 688, in run
  │   →     test_driver_message = self.get_next_message(url, script_resume, test_window)
  │   →                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 732, in get_next_message
  │   →     return self._get_next_message_classic(url, script_resume)
  │   →            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 739, in _get_next_message_classic
  │   →     return self.parent.base.execute_script(script_resume, asynchronous=True, args=[strip_server(url)])
  │   →            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorwebdriver.py", line 81, in execute_script
  │   →     return method(script, args=args)
  │   →            ^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/webdriver/webdriver/client.py", line 780, in execute_async_script
  │   →     return self.send_session_command("POST", "execute/async", body)
  │   →            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/webdriver/webdriver/client.py", line 650, in send_session_command
  │   →     return self.send_command(method, url, body, timeout)
  │   →            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  │   →   File "/home/runner/work/servo/servo/tests/wpt/tests/tools/webdriver/webdriver/client.py", line 605, in send_command
  │   →     raise err
  │   → webdriver.error.JavascriptErrorException: javascript error (500): window.__wptrunner_process_next_event is not a function
  │   → 
  │   → Remote-end stacktrace:
  │   → 
  │   → @:8:8
  │   → @:10:21
  │   → @:2:17
  └   → @:15:15