The same error happens on other webrtc autotests before, crbug.com/766769.
Perhaps it would be helpful to see how they fixed this.

[Log]
https://stainless.corp.google.com/browse/chromeos-autotest-results/210623499-chromeos-test/chromeos2-row4-rack7-host7/

Traceback (most recent call last):
  File "/usr/local/autotest/common_lib/test.py", line 831, in _call_test_function
    return func(*args, **dargs)
  File "/usr/local/autotest/common_lib/test.py", line 495, in execute
    dargs)
  File "/usr/local/autotest/common_lib/test.py", line 362, in _call_run_once_with_retry
    postprocess_profiled_run, args, dargs)
  File "/usr/local/autotest/common_lib/test.py", line 400, in _call_run_once
    self.run_once(*args, **dargs)
  File "/usr/local/autotest/cros/video/helper_logger.py", line 82, in call
    return func(*args, **kwargs)
  File "/usr/local/autotest/tests/video_WebRtcMediaRecorder/video_WebRtcMediaRecorder.py", line 94, in run_once
    self.launch_recorder_test('testIllegalResumeThrowsDOMError')
  File "/usr/local/autotest/tests/video_WebRtcMediaRecorder/video_WebRtcMediaRecorder.py", line 48, in launch_recorder_test
    if not self.is_test_completed():
  File "/usr/local/autotest/tests/video_WebRtcMediaRecorder/video_WebRtcMediaRecorder.py", line 78, in is_test_completed
    sleep_interval=1)
  File "/usr/local/autotest/common_lib/utils.py", line 2615, in poll_for_condition
    value = condition()
  File "/usr/local/autotest/tests/video_WebRtcMediaRecorder/video_WebRtcMediaRecorder.py", line 71, in test_done
    test_progress = self.tab.EvaluateJavaScript(TEST_PROGRESS)
  File "/usr/local/telemetry/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
    return func(*args, **kwargs)
  File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/browser/web_contents.py", line 215, in EvaluateJavaScript
    return self._inspector_backend.EvaluateJavaScript(*args, **kwargs)
  File "/usr/local/telemetry/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
    return func(*args, **kwargs)
  File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py", line 252, in EvaluateJavaScript
    return self._EvaluateJavaScript(expression, context_id, timeout)
  File "/usr/local/telemetry/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 52, in traced_function
    return func(*args, **kwargs)
  File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py", line 38, in Inner
    return func(inspector_backend, *args, **kwargs)
  File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py", line 519, in _EvaluateJavaScript
    return self._runtime.Evaluate(expression, context_id, timeout)
  File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_runtime.py", line 53, in Evaluate
    description=details.get('exception', {}).get('description'))
EvaluateException: UncaughtReferenceError:
ReferenceError: testProgress is not defined