This race is caught by every test that overrides InProcessBrowserTest::SetUp() to do something before if that something does logging (e.g. virtually all).

This race is also real in the product. If any thread (including main thread) calls SetMinLogLevel() at any point, it races with any log statement trying to GetMinLogLevel().

As usual, there is no such thing as benign data race: 
https://software.intel.com/en-us/blogs/2013/01/06/benign-data-races-what-could-possibly-go-wrong

This is a prerequisite to enabling TSAN for browser_tests.

Log:

WARNING: ThreadSanitizer: data race (pid=9471)
  Write of size 4 at 0x0000106c47d0 by main thread:
    #0 logging::SetMinLogLevel(int) base/logging.cc:412:19 (browser_tests+0x4256c1b)
    #1 logging::InitChromeLogging(base::CommandLine const&, logging::OldFileDeletionState) chrome/common/logging_chrome.cc:325:7 (browser_tests+0x5e28b4f)
    #2 InitLogging chrome/app/chrome_main_delegate.cc:487:3 (browser_tests+0x5e0cb00)
    #3 ChromeMainDelegate::PreSandboxStartup() chrome/app/chrome_main_delegate.cc:837 (browser_tests+0x5e0cb00)
    #4 content::ContentMainRunnerImpl::Initialize(content::ContentMainParams const&) content/app/content_main_runner.cc:638:18 (browser_tests+0x41f3a05)
    #5 content::ContentServiceManagerMainDelegate::Initialize(service_manager::MainDelegate::InitializeParams const&) content/app/content_service_manager_main_delegate.cc:37:32 (browser_tests+0x41f15a4)
    #6 service_manager::Main(service_manager::MainParams const&) services/service_manager/embedder/main.cc:426:29 (browser_tests+0x7035226)
    #7 content::ContentMain(content::ContentMainParams const&) content/app/content_main.cc:19:10 (browser_tests+0x41f1fcb)
    #8 content::BrowserTestBase::SetUp() content/public/test/browser_test_base.cc:271:3 (browser_tests+0x4d46146)
    #9 InProcessBrowserTest::SetUp() chrome/test/base/in_process_browser_test.cc:271:20 (browser_tests+0x43939d0)
    #10 HistoryBrowserTest::SetUp() chrome/browser/history/history_browsertest.cc:56:27 (browser_tests+0x8bae07)
    (...)
  Previous read of size 4 at 0x0000106c47d0 by thread T1:
    #0 GetMinLogLevel base/logging.cc:416:10 (browser_tests+0x4256ddc)
    #1 GetVlogVerbosity base/logging.cc:431 (browser_tests+0x4256ddc)
    #2 logging::GetVlogLevelHelper(char const*, unsigned long) base/logging.cc:441 (browser_tests+0x4256ddc)
    #3 GetVlogLevel<35> base/logging.h:261:10 (browser_tests+0x51854a0)
    #4 net::MapSystemError(int) net/base/net_errors_posix.cc:18 (browser_tests+0x51854a0)
    #5 MapAcceptError net/socket/socket_posix.cc:38:14 (browser_tests+0x527cd91)
    #6 net::SocketPosix::DoAccept(std::__1::unique_ptr<net::SocketPosix, std::__1::default_delete<net::SocketPosix> >*) net/socket/socket_posix.cc:422 (browser_tests+0x527cd91)
    #7 net::SocketPosix::Accept(std::__1::unique_ptr<net::SocketPosix, std::__1::default_delete<net::SocketPosix> >*, base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) net/socket/socket_posix.cc:166:12 (browser_tests+0x527cb8a)
    #8 net::TCPSocketPosix::Accept(std::__1::unique_ptr<net::TCPSocketPosix, std::__1::default_delete<net::TCPSocketPosix> >*, net::IPEndPoint*, base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) net/socket/tcp_socket_posix.cc:231:21 (browser_tests+0x50d6d57)
    #9 net::TCPServerSocket::Accept(std::__1::unique_ptr<net::StreamSocket, std::__1::default_delete<net::StreamSocket> >*, base::Callback<void (int), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) net/socket/tcp_server_socket.cc:73:24 (browser_tests+0x50d5af1)
    #10 net::test_server::EmbeddedTestServer::DoAcceptLoop() net/test/embedded_test_server/embedded_test_server.cc:347:26 (browser_tests+0x5355961)
    (...)
  Location is global 'logging::(anonymous namespace)::g_min_log_level' of size 4 at 0x0000106c47d0 (browser_tests+0x0000106c47d0)
  Thread T1 'EmbeddedTestServer IO Thread' (tid=9513, running) created by main thread at:
    #0 pthread_create <null> (browser_tests+0x58d6b3)
    #1 base::(anonymous namespace)::CreateThread(unsigned long, bool, base::PlatformThread::Delegate*, base::PlatformThreadHandle*, base::ThreadPriority) base/threading/platform_thread_posix.cc:110:13 (browser_tests+0x42ee166)
    #2 base::PlatformThread::CreateWithPriority(unsigned long, base::PlatformThread::Delegate*, base::PlatformThreadHandle*, base::ThreadPriority) base/threading/platform_thread_posix.cc:193:10 (browser_tests+0x42ee025)
    #3 base::Thread::StartWithOptions(base::Thread::Options const&) base/threading/thread.cc:112:15 (browser_tests+0x42f9b53)
    #4 net::test_server::EmbeddedTestServer::StartAcceptingConnections() net/test/embedded_test_server/embedded_test_server.cc:172:3 (browser_tests+0x5354b3d)
    #5 net::test_server::EmbeddedTestServer::Start() net/test/embedded_test_server/embedded_test_server.cc:89:3 (browser_tests+0x5354285)
    #6 HistoryBrowserTest::SetUp() chrome/browser/history/history_browsertest.cc:55:5 (browser_tests+0x8badf0)
    (...)
SUMMARY: ThreadSanitizer: data race base/logging.cc:412:19 in logging::SetMinLogLevel(int)