On multiple platforms, ExternalProtocolHandlerTests will fail or crash on the first attempt before succeeding on the second: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=unit_tests&tests=ExternalProtocolHandlerTest

On rare occasions, this can happen more than once in a single run, resulting in a visible failure: https://luci-milo.appspot.com/buildbot/chromium.linux/Android%20Tests/44547

Failures can come from any of the three ASSERT_TRUEs here: https://codesearch.chromium.org/chromium/src/chrome/browser/external_protocol/external_protocol_handler_unittest.cc?rcl=b0a8dabdd22a2b9ecc755ac7deaad22bee218da9&l=135

while crashes frequently look something like this:

	base::internal::TaskTracker::BeforePostTask [0x03287DAC+12]

	base::internal::TaskTracker::WillPostTask [0x03287D4E+30]

	base::internal::SchedulerSingleThreadTaskRunnerManager::SchedulerSingleThreadTaskRunner::PostDelayedTask [0x032AD79E+110]

	base::TaskRunner::PostTask [0x03215B93+67]

	shell_integration::DefaultWebClientWorker::StartCheckIsDefault [0x04354C51+187]

	ExternalProtocolHandler::LaunchUrlWithDelegate [0x03407088+402]

	ExternalProtocolHandlerTest::DoTest [0x011A27D6+578]

	ExternalProtocolHandlerTest_TestLaunchSchemeUnknownChromeUnknown_Test::TestBody [0x011A30F5+21]

(source: https://chromium-swarm.appspot.com/task?id=37db47c9a04c5210)