On 6/24, a number of Kiosk browser tests started DCHECKing and failing on Linux ChromiumOS Tests (dbg).  The DCHECK is
    DCHECK(!visible_ || layer()->GetTargetOpacity() > 0.0f);
in Window::Show():
https://cs.chromium.org/chromium/src/ui/aura/window.cc?q=Window::Show&sq=package:chromium&dr=CSs&l=235

See recent failures in
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%28dbg%29%281%29?numbuilds=200

Some tests observed to have failed in this specific way are:

KioskUpdateTest.IncompliantPlatformFirstInstall
KioskUpdateTest.LaunchAppWithSecondaryArcLikeAppAndExtension
KioskUpdateTest.LaunchAppWithSharedModuleAndSecondaryApp
KioskUpdateTest.LaunchKioskAppWithSecondaryExtension
KioskUpdateTest.PRE_LaunchAppWithUpdatedModule
KioskUpdateTest.PRE_UpdateMultiAppKioskAddOneApp
KioskUpdateTest.PRE_UpdateMultiAppKioskRemoveOneApp
KioskEnterpriseTest.PrivateStore

... and so forth.  The problem always happens when the test calls WaitForAppLaunchWithOptions().  The message loop runs StartupAppLauncher::OnReadyToLaunch(), which leads to Shell::ShowShelf(), and Widget::Show() on the StatusAreaWidget; then the NativeWidgetAura calls window_->Show().

When I traced through this, the StatusAreaWidget's Show() function was called 47 times. Regarding the DCHECK conditions: sometimes the window_ was visible and opacity was 1; sometimes it wasn't visible, and opacity was 1.  On the Show() call right before the DCHECK, it wasn't visible, and opacity was 0.  When it DCHECKED, of course, it was now visible, but opacity was still 0.  Note that this this doesn't always happen... sometimes these tests pass.  So whatever is showing and hiding this window and setting its opacity is doing it in a non-deterministic order.

I don't know if this is related to  Issue 612688 .  Those aren't running on (dbg), and the errors seem different.

Here's the call stack:

#1 logging::LogMessage::~LogMessage()
#2 aura::Window::Show()
#3 views::NativeWidgetAura::ShowWithWindowState()
#4 views::Widget::Show()
#5 ash::RootWindowController::ShowShelf()
#6 ash::Shell::ShowShelf()
#7 ChromeShellDelegate::Observe()
#8 content::NotificationServiceImpl::Notify()
#9 chromeos::ChromeUserManagerImpl::SessionStarted()
#10 chromeos::StartupAppLauncher::LaunchApp()
#11 chromeos::AppLaunchController::OnReadyToLaunch()
#12 chromeos::StartupAppLauncher::OnReadyToLaunch()
#13 base*internal*RunnableAdapter*CancelableCallback*Run*WeakPtr*
#14 base*internal*InvokeHelper*MakeItSo*RunnableAdapter*CancelableCallback*WeakPtr*
#15 base*internal*Invoker*IndexSequence*BindState*RunnableAdapter*chromeos*StartupAppLauncher*WeakPtr*BindStateBase*
#16 base::Callback<>::Run()
#17 base::debug::TaskAnnotator::RunTask()
#18 base::MessageLoop::RunTask()
#19 base::MessageLoop::DeferOrRunPendingTask()
#20 base::MessageLoop::DoWork()
#21 base::MessagePumpGlib::Run()
#22 base::MessageLoop::RunHandler()
#23 base::RunLoop::Run()
#24 content::RunThisRunLoop()
#25 content::MessageLoopRunner::Run()
#26 content::WindowedNotificationObserver::Wait()
#27 chromeos::KioskTest::WaitForAppLaunchWithOptions()
#28 chromeos::KioskEnterpriseTest_PrivateStore_Test::RunTestOnMainThread() (for example)

... more to come...