This seems to fail about 2% of runs.

Traceback (most recent call last):
  _RunGpuTest at content/test/gpu/gpu_tests/gpu_integration_test.py:125
    self.RunActualGpuTest(url, *args)
  RunActualGpuTest at content/test/gpu/gpu_tests/maps_integration_test.py:126
    screenshot = tab.Screenshot(5)
  traced_function at third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  Screenshot at third_party/catapult/telemetry/telemetry/internal/browser/tab.py:117
    return self._inspector_backend.Screenshot(timeout)
  traced_function at third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  inner at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py:39
    inspector_backend._ConvertExceptionFromInspectorWebsocket(e)
  traced_function at third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  inner at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py:36
    return func(inspector_backend, *args, **kwargs)
  Screenshot at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend.py:142
    return self._page.CaptureScreenshot(timeout)
  CaptureScreenshot at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_page.py:153
    res = self._inspector_websocket.SyncRequest(request, timeout)
  SyncRequest at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_websocket.py:110
    res = self._Receive(timeout)
  _Receive at third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_websocket.py:149
    data = self._socket.recv()
  recv at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:293
    opcode, data = self.recv_data()
  recv_data at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:310
    opcode, frame = self.recv_data_frame(control_frame)
  recv_data_frame at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:323
    frame = self.recv_frame()
  recv_frame at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:357
    return self.frame_buffer.recv_frame()
  recv_frame at third_party/catapult/telemetry/third_party/websocket-client/websocket/_abnf.py:336
    self.recv_header()
  recv_header at third_party/catapult/telemetry/third_party/websocket-client/websocket/_abnf.py:286
    header = self.recv_strict(2)
  recv_strict at third_party/catapult/telemetry/third_party/websocket-client/websocket/_abnf.py:371
    bytes_ = self.recv(min(16384, shortage))
  _recv at third_party/catapult/telemetry/third_party/websocket-client/websocket/_core.py:427
    return recv(self.sock, bufsize)
  recv at third_party/catapult/telemetry/third_party/websocket-client/websocket/_socket.py:83
    raise WebSocketTimeoutException(message)
TimeoutException: 

It looks like it's timing out trying to take a screenshot.

For example, the 10 most recent failures:
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68776
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68765
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68749
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68705
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68611
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68580
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68532
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68510
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68443
https://build.chromium.org/p/chromium.gpu/builders/Mac%20Release%20%28Intel%29/builds/68322