CaptivePortalBrowserTest.LoginExtraNavigations flaky crash in mus_browser_tests

This test failed for one trybot run on my CL, but not the other; I can't repro locally.
I don't think I'm introducing flakiness here, but don't see failures on the flakiness dashboard.

https://build.chromium.org/deprecated/tryserver.chromium.chromiumos/builders/linux-chromeos-rel/builds/75525/steps/mus_browser_tests%20(with%20patch)/logs/CaptivePortalBrowserTest.LoginExtraNavigations

[31579:31579:0308/141547.200189:FATAL:surface_manager.cc(78)] Check failed: surface_map_.empty(). 
#0 0x0000041fba7c base::debug::StackTrace::StackTrace()
#1 0x0000042167ac logging::LogMessage::~LogMessage()
#2 0x00000613cd5d viz::SurfaceManager::~SurfaceManager()
#3 0x000006119618 viz::FrameSinkManagerImpl::~FrameSinkManagerImpl()
#4 0x00000611978e viz::FrameSinkManagerImpl::~FrameSinkManagerImpl()
#5 0x000002a26bbc content::BrowserMainLoop::ShutdownThreadsAndCleanUp()
#6 0x000002a297d3 content::BrowserMainRunnerImpl::Shutdown()
#7 0x000002a22646 content::BrowserMain()
#8 0x0000041c7fde content::ContentMainRunnerImpl::Run()
#9 0x000006254464 service_manager::Main()
#10 0x0000041c6604 content::ContentMain()
#11 0x00000483e8ff content::BrowserTestBase::SetUp()
#12 0x00000430b60f InProcessBrowserTest::SetUp()
#13 0x000001d69561 testing::Test::Run()
#14 0x000001d6a130 testing::TestInfo::Run()
#15 0x000001d6a617 testing::TestCase::Run()
#16 0x000001d75637 testing::internal::UnitTestImpl::RunAllTests()
#17 0x000001d751be testing::UnitTest::Run()
#18 0x00000431fb52 base::TestSuite::Run()
#19 0x0000041ef865 ChromeTestSuiteRunner::RunTestSuite()
#20 0x000004871b98 content::LaunchTests()
#21 0x0000041efd24 LaunchChromeTests()
#22 0x0000041ef7fe main
#23 0x7f38278d9f45 __libc_start_main
#24 0x0000005cf3ea _start