Seen this across these builds just recently:

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Release%20(AMD)/7586
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Release%20(AMD)/7593
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Retina%20Release%20(AMD)/7596

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Experimental%20Retina%20Release%20(AMD)/4972

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20Retina%20Debug%20(AMD)/33127

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20Retina%20Release%20(AMD)/40089
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20Retina%20Release%20(AMD)/40103

Apparently it's prevalent on these Mac Retina AMD bots.

One stack trace (from 7596):

Traceback (most recent call last):
  <module> at /b/s/w/ir/third_party/catapult/telemetry/telemetry/testing/run_browser_tests.py:359
    ret_code = RunTests(sys.argv[1:])
  RunTests at /b/s/w/ir/third_party/catapult/telemetry/telemetry/testing/run_browser_tests.py:328
    ret, _, _ = runner.run()
  run at /b/s/w/ir/third_party/catapult/third_party/typ/typ/runner.py:179
    ret, full_results = self._run_tests(result_set, test_set)
  _run_tests at /b/s/w/ir/third_party/catapult/third_party/typ/typ/runner.py:466
    self._run_one_set(self.stats, result_set, test_set)
  _run_one_set at /b/s/w/ir/third_party/catapult/third_party/typ/typ/runner.py:511
    test_set.isolated_tests, 1)
  _run_list at /b/s/w/ir/third_party/catapult/third_party/typ/typ/runner.py:537
    _setup_process, _teardown_process)
  make_pool at /b/s/w/ir/third_party/catapult/third_party/typ/typ/pool.py:28
    return _AsyncPool(host, jobs, callback, context, pre_fn, post_fn)
  __init__ at /b/s/w/ir/third_party/catapult/third_party/typ/typ/pool.py:188
    self.context_after_pre = pre_fn(self.host, 1, self.context)
  _setup_process at /b/s/w/ir/third_party/catapult/third_party/typ/typ/runner.py:807
    child.context_after_setup = child.setup_fn(child, child.context)
  _SetUpProcess at /b/s/w/ir/third_party/catapult/telemetry/telemetry/testing/run_browser_tests.py:349
    context.test_class.SetUpProcess()
  SetUpProcess at /b/s/w/ir/content/test/gpu/gpu_tests/webgl_conformance_integration_test.py:297
    cls.StartBrowser()
  StartBrowser at /b/s/w/ir/content/test/gpu/gpu_tests/gpu_integration_test.py:96
    cls.tab = cls.browser.tabs[0]
  __getitem__ at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/browser/tab_list.py:18
    return self._tab_list_backend.__getitem__(index)
  __getitem__ at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend_list.py:56
    self._Update()
  _Update at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/inspector_backend_list.py:99
    backends_map = self._devtools_client.GetUpdatedInspectableContexts()
  GetUpdatedInspectableContexts at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py:399
    contexts = self._ListInspectableContexts()
  _ListInspectableContexts at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/devtools_client_backend.py:324
    return self._devtools_http.RequestJson('')
  RequestJson at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/devtools_http.py:107
    return json.loads(self.Request(path, timeout))
  Request at /b/s/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome_inspector/devtools_http.py:88
    response = self._conn.getresponse()
  getresponse at /b/s/w/ir/.swarming_module/lib/python2.7/httplib.py:1121
    response.begin()
  begin at /b/s/w/ir/.swarming_module/lib/python2.7/httplib.py:438
    version, status, reason = self._read_status()
  _read_status at /b/s/w/ir/.swarming_module/lib/python2.7/httplib.py:394
    line = self.fp.readline(_MAXLINE + 1)
  readline at /b/s/w/ir/.swarming_module/lib/python2.7/socket.py:480
    data = self._sock.recv(self._rbufsize)
DevToolsClientConnectionError: timed out