To reproduce: Run chrome (or browser_tests) under KDE on Linux. Exit the process.

Expected behaviour: Doesn't CHECK fail on shutdown
Actual behaviour:

[120208:120208:0112/222910.742870:FATAL:file_descriptor_watcher_posix.cc(29)] Check failed: sequence_checker_.CalledOnValidSequence(). 
#0 0x0000050a89bc base::debug::StackTrace::StackTrace()
#1 0x0000050c8aec logging::LogMessage::~LogMessage()
#2 0x0000050aee02 base::FileDescriptorWatcher::Controller::~Controller()
#3 0x00000594314e net::(anonymous namespace)::SettingGetterImplKDE::~SettingGetterImplKDE()
#4 0x00000594329e net::(anonymous namespace)::SettingGetterImplKDE::~SettingGetterImplKDE()
#5 0x00000593d62a net::ProxyConfigServiceLinux::Delegate::~Delegate()
#6 0x0000059404b7 net::ProxyConfigServiceLinux::~ProxyConfigServiceLinux()
#7 0x0000059404ee net::ProxyConfigServiceLinux::~ProxyConfigServiceLinux()
#8 0x0000071dd17a ProxyConfigServiceImpl::~ProxyConfigServiceImpl()
#9 0x0000052a9ea8 ProxyConfigMonitor::~ProxyConfigMonitor()
#10 0x0000051ead41 BrowserProcessImpl::PostDestroyThreads()
#11 0x0000051e9bbb ChromeBrowserMainParts::PostDestroyThreads()
#12 0x000003a4aa73 content::BrowserMainLoop::ShutdownThreadsAndCleanUp()
#13 0x000003a4d36d content::BrowserMainRunnerImpl::Shutdown()
#14 0x000003a457d6 content::BrowserMain()
#15 0x0000050877eb content::RunNamedProcessTypeMain()
#16 0x0000050882c6 content::ContentMainRunnerImpl::Run()
#17 0x000006ff0064 service_manager::Main()
#18 0x000005086b31 content::ContentMain()
#19 0x0000057030ae content::BrowserTestBase::SetUp()
#20 0x000005182e3b InProcessBrowserTest::SetUp()
#21 0x0000030dceb1 testing::Test::Run()
#22 0x0000030dd9e0 testing::TestInfo::Run()
#23 0x0000030ddec7 testing::TestCase::Run()
#24 0x0000030e44f7 testing::internal::UnitTestImpl::RunAllTests()
#25 0x0000030e4177 testing::UnitTest::Run()
#26 0x000005198982 base::TestSuite::Run()
#27 0x00000509b142 ChromeTestSuiteRunner::RunTestSuite()
#28 0x00000573c609 content::LaunchTests()
#29 0x00000509b511 LaunchChromeTests()
#30 0x00000509b09e main
#31 0x7f560a0aef45 __libc_start_main
#32 0x000001f5d02a _start

git bisect indicates culprit:

d0d0d0508a541932ce4e43dfdeec1eb6dacf9edf is the first bad commit
commit d0d0d0508a541932ce4e43dfdeec1eb6dacf9edf
Author: Matt Menke <mmenke@chromium.org>
Date:   Fri Dec 1 19:00:50 2017 +0000

    Send proxy configuration over Mojo pipe in Chrome.
    
    Do this by moving ProxyConfigService creation and ownership
    from the legacy IOThread/ProfileIOData classes on the IO thread
    to a new ProxyConfigMonitor class, which lives on the UI thread
    and is owned by the new SystemNetworkContextManager and
    ProfileNetworkContextService classes.
    
    Chrome's ProxyConfigService now sends messages to the network
    stack over a Mojo pipe from the UI thread over to the IO thread
    (or the network process) instead of plugging directly in to the
    ProxyService on the IO thread.
    
    This effectively adds support for non-PAC proxy configurations
    when the network service is enabled.
    
    This CL also makes NetworkContext default to using direct
    connections, instead of the system proxy configuration, both
    to ensure a NetworkContext can always successfully be created,
    and because it's more sandbox friendly.  Included in this CL
    because without it, tests fail on Linux and ChromeOS when the
    network service is enabled, because the legacy in-process
    URLRequestContextBuilder can't create a ProxyConfigService on
    those platforms.
    
    Bug:  754007 
    Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.linux:linux_mojo;master.tryserver.chromium.mac:ios-simulator-cronet
    Change-Id: I537514ae8bf3726b3215bcf9b9b27f2d8ae2a951
    Reviewed-on: https://chromium-review.googlesource.com/760538
    Commit-Queue: Matt Menke <mmenke@chromium.org>
    Reviewed-by: Eric Roman <eroman@chromium.org>
    Reviewed-by: Scott Violet <sky@chromium.org>
    Reviewed-by: Tom Sepez <tsepez@chromium.org>
    Reviewed-by: John Abd-El-Malek <jam@chromium.org>
    Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#521003}