Example run:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/ios-simulator-full-configs/10011

Flakiness dashboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=ios_chrome_ui_egtests&builder=chromium.mac%3Aios-simulator-full-configs-iPhone%20X-12.0


Stack trace:
DownloadManagerTestCase/testSucessfullDownload:
[1031/125601.024332:WARNING:embedded_test_server.cc(239)] Request not handled. Returning 404: /favicon.ico
[1031/125610.838936:FATAL:url_fetcher_response_writer.cc(135)] Check failed: !callback_.
0   ios_chrome_ui_egtests               0x00000001054f32fd base::debug::StackTrace::StackTrace(unsigned long) + 157
1   ios_chrome_ui_egtests               0x00000001054f333d base::debug::StackTrace::StackTrace(unsigned long) + 29
2   ios_chrome_ui_egtests               0x00000001051c643a base::debug::StackTrace::StackTrace() + 26
3   ios_chrome_ui_egtests               0x000000010520952d logging::LogMessage::~LogMessage() + 461
4   ios_chrome_ui_egtests               0x00000001052071d5 logging::LogMessage::~LogMessage() + 21


Not sure what's the right component, so adding a couple of them.