This has been happening on and off for a couple days. The ash process is crashing.

Test: desktopui_MashLogin.
Suite: bvt-perbuild.
Chrome Version: 69.0.3451.0.
Build: scarlet-arcnext-release/R69-10758.0.0.

Reason:
Unhandled BrowserGoneException: [Errno 111] Connection refused.
build artifacts:
https://storage.cloud.google.com/?arg=chromeos-image-archive/scarlet-arcnext-release/R69-10758.0.0.
results log: http://ubercautotest.corp.google.com/tko/retrieve_logs.cgi?job=/results/206149667-chromeos-test/chromeos2-row2-rack11-host15/debug/.
status log: http://ubercautotest.corp.google.com/tko/retrieve_logs.cgi?job=/results/206149667-chromeos-test/chromeos2-row2-rack11-host15/status.log.
job link: http://cautotest-prod/afe/#tab_id=view_job&object_id=206149667.

Crash reason:  SIGSEGV
Crash address: 0x0
Process uptime: not available

Thread 0 (crashed)
 0  chrome!ash::ImmersiveFullscreenController::IsEnabled() const [immersive_fullscreen_controller.cc : 147 + 0x0]
     r0 = 0x00000000    r1 = 0x0398ee2b    r2 = 0x00000000    r3 = 0x0be47b70
     r4 = 0x0bdf1940    r5 = 0x09f815a0    r6 = 0x09a803c0    r7 = 0xffa11a28
     r8 = 0xffa11a34    r9 = 0xf7008ec0   r10 = 0x00000000   r12 = 0x03cf8a13
     fp = 0xffa11a88    sp = 0xffa11a18    lr = 0x066a6133    pc = 0x03cf8a12
    Found by: given as instruction pointer in context
 1  chrome!ash::(anonymous namespace)::CustomFrameViewAshWindowStateDelegate::OnPostWindowStateTypeChange(ash::wm::WindowState*, ash::mojom::WindowStateType) [custom_frame_view_ash.cc : 149 + 0x3]
     r4 = 0x0bdf1940    r5 = 0x09f815a0    r6 = 0x09a803c0    r7 = 0xffa11a28
     r8 = 0xffa11a34    r9 = 0xf7008ec0   r10 = 0x00000000    fp = 0xffa11a88
     sp = 0xffa11a18    pc = 0x066a6133
    Found by: call frame info
 2  chrome!ash::wm::WindowState::NotifyPostStateTypeChange(ash::mojom::WindowStateType) [window_state.cc : 586 + 0x7]
     r4 = 0x00000003    r5 = 0x09f815a0    r6 = 0xffa11a44    r7 = 0xffa11a70
     r8 = 0xffa11a34    r9 = 0xf7008ec0   r10 = 0x00000000    fp = 0xffa11a88
     sp = 0xffa11a30    pc = 0x06730695
    Found by: call frame info
 3  chrome!ash::wm::DefaultState::EnterToNextState(ash::wm::WindowState*, ash::mojom::WindowStateType) [default_state.cc : 451 + 0x7]
     r4 = 0x09f815a0    r5 = 0x09567620    r6 = 0x00000000    r7 = 0xffa11b70
     r8 = 0x00000003    r9 = 0xf7008ec0   r10 = 0xffa11aa8    fp = 0xffa11a88
     sp = 0xffa11a78    pc = 0x0679a7df
    Found by: call frame info
 4  chrome!ash::wm::DefaultState::HandleTransitionEvents(ash::wm::WindowState*, ash::wm::WMEvent const*) [default_state.cc : 367 + 0x9]
     r4 = 0x09f815a0    r5 = 0x00000003    r6 = 0xffa11c3c    r7 = 0xffa11c30
     r8 = 0x09567620    r9 = 0x00000000   r10 = 0xf7008ec0    fp = 0x08f042d0
     sp = 0xffa11b78    pc = 0x0679a62d
    Found by: call frame info
 5  chrome!ash::wm::WindowState::OnWindowPropertyChanged(aura::Window*, void const*, int) [window_state.cc : 322 + 0x3]
     r4 = 0x09f815a0    r5 = 0xffa11c3c    r6 = 0x09a92240    r7 = 0xffa11c58
     r8 = 0xf7008ec0    r9 = 0xffa11c64   r10 = 0xf7008ec0    fp = 0x08f042d0
     sp = 0xffa11c38    pc = 0x06730c35
    Found by: call frame info
 6  chrome!aura::Window::AfterPropertyChange(void const*, long long, std::__1::unique_ptr<ui::PropertyData, std::__1::default_delete<ui::PropertyData> >) [window.cc : 730 + 0x7]
     r4 = 0xffa11c74    r5 = 0x06730b11    r6 = 0x09a92240    r7 = 0xffa11ca8
     r8 = 0x00000000    r9 = 0xffa11c64   r10 = 0xf7008ec0    fp = 0x08f042d0
     sp = 0xffa11c60    pc = 0x05d5c58b
    Found by: call frame info
 7  chrome!ui::PropertyHandler::SetPropertyInternal(void const*, char const*, void (*)(long long), long long, long long) [class_property.cc : 35 + 0x5]
     r4 = 0x08f042d0    r5 = 0x00000000    r6 = 0x05d5c5cd    r7 = 0xffa11ce8
     r8 = 0x00000000    r9 = 0x00000000   r10 = 0x09a92274    fp = 0x0b884bd0
     sp = 0xffa11cb0    pc = 0x056d8041
    Found by: call frame info
 8  chrome!aura::PropertyConverter::SetPropertyFromTransportValue(aura::Window*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::vector<unsigned char, std::__1::allocator<unsigned char> > const*) [property_converter.cc : 218 + 0x11]
     r4 = 0x00000003    r5 = 0x00000000    r6 = 0x08850d31    r7 = 0xffa11d58
     r8 = 0x09512630    r9 = 0x0950fc00   r10 = 0x0950fc04    fp = 0xffa11dd8
     sp = 0xffa11cf0    pc = 0x05d6c16d
    Found by: call frame info
 9  chrome!aura::WindowTreeClient::WmSetProperty(unsigned int, unsigned long long, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, base::Optional<std::__1::vector<unsigned char, std::__1::allocator<unsigned char> > > const&) [window_tree_client.cc : 2034 + 0x7]
     r4 = 0x0950fc00    r5 = 0xffa11dd8    r6 = 0x00000001    r7 = 0xffa11d88
     r8 = 0xf7008ec0    r9 = 0x0a260908   r10 = 0x094b2d80    fp = 0x0000000a
     sp = 0xffa11d60    pc = 0x05d563a1
    Found by: call frame info
10  chrome!ui::mojom::WindowManagerStubDispatch::Accept(ui::mojom::WindowManager*, mojo::Message*) [window_manager.mojom.cc : 1281 + 0xb]
     r4 = 0xffa11dac    r5 = 0x05d563d1    r6 = 0xffa11db0    r7 = 0xffa11ec8
     r8 = 0x00000001    r9 = 0x0000000a   r10 = 0x094b2d84    fp = 0xf7008ec0
     sp = 0xffa11d90    pc = 0x03ce4949
    Found by: call frame info
11  chrome!mojo::InterfaceEndpointClient::HandleIncomingMessageThunk::Accept(mojo::Message*) [interface_endpoint_client.cc : 419 + 0x7]
     r4 = 0xf7008ec0    r5 = 0xffa11ff0    r6 = 0xffa11ff4    r7 = 0xffa11f00
     r8 = 0x09510e00    r9 = 0xf7008ec0   r10 = 0xffa11f0c    fp = 0x0951f280
     sp = 0xffa11ed0    pc = 0x037d11a3
    Found by: call frame info
12  chrome!mojo::internal::MultiplexRouter::ProcessIncomingMessage(mojo::internal::MultiplexRouter::MessageWrapper*, mojo::internal::MultiplexRouter::ClientCallBehavior, base::SequencedTaskRunner*) [multiplex_router.cc : 865 + 0x5]
     r4 = 0xf7008ec0    r5 = 0xffa11ff0    r6 = 0xffa11ff4    r7 = 0xffa11f60
     r8 = 0x09510e00    r9 = 0x09510f20   r10 = 0x0951f280    fp = 0x00000000
     sp = 0xffa11f08    pc = 0x05123635
    Found by: call frame info
13  chrome!mojo::internal::MultiplexRouter::Accept(mojo::Message*) [multiplex_router.cc : 589 + 0x7]
     r4 = 0x09510e00    r5 = 0x00000002    r6 = 0xffa11fbc    r7 = 0xffa12048
     r8 = 0x00000000    r9 = 0x00000000   r10 = 0xf7008ec0    fp = 0xffa11ff4
     sp = 0xffa11f68    pc = 0x037d1263
    Found by: call frame info
14  chrome!mojo::Connector::ReadSingleMessage(unsigned int*) [connector.cc : 443 + 0x7]
     r4 = 0x09510e30    r5 = 0x0914d278    r6 = 0x0918c2e0    r7 = 0xffa120e0
     r8 = 0xf7008ec0    r9 = 0xffa120ec   r10 = 0xf7008ec0    fp = 0xf7008ec0
     sp = 0xffa12050    pc = 0x037d0dc5
    Found by: call frame info
15  chrome!mojo::Connector::ReadAllAvailableMessages() [connector.cc : 472 + 0x5]
     r4 = 0x09510e30    r5 = 0x09510f0c    r6 = 0xffa120f4    r7 = 0xffa12118
     r8 = 0xffa120f0    r9 = 0xffa120ec   r10 = 0xf7008ec0    fp = 0xf7008ec0
     sp = 0xffa120e8    pc = 0x037d0f45
    Found by: call frame info
16  chrome!mojo::SimpleWatcher::OnHandleReady(int, unsigned int, mojo::HandleSignalsState const&) [callback.h : 125 + 0x1]
     r4 = 0x09524ae0    r5 = 0xffa12128    r6 = 0xffa12134    r7 = 0xffa12158
     r8 = 0x0918bc8c    r9 = 0x0bcbbad8   r10 = 0x00000000    fp = 0xf7008ec0
     sp = 0xffa12120    pc = 0x037d1a3d
    Found by: call frame info
17  chrome!base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) [callback.h : 96 + 0x1]
     r4 = 0xffa12240    r5 = 0x00000000    r6 = 0xffa1216c    r7 = 0xffa121b8
     r8 = 0x09508f28    r9 = 0xf7008ec0   r10 = 0x084cf478    fp = 0xffa12240
     sp = 0xffa12160    pc = 0x037c9c05
    Found by: call frame info
18  chrome!base::MessageLoop::RunTask(base::PendingTask*) [message_loop.cc : 319 + 0x5]
     r4 = 0x085d1b04    r5 = 0xffa121d8    r6 = 0xffa121e8    r7 = 0xffa12230
     r8 = 0x00000000    r9 = 0xffa12478   r10 = 0x0918bc8c    fp = 0xffa12240
     sp = 0xffa121c0    pc = 0x037ca3c9
    Found by: call frame info
19  chrome!base::MessageLoop::DoWork() [message_loop.cc : 329 + 0x7]
     r4 = 0xffa12478    r5 = 0xffa12240    r6 = 0xf7008ec0    r7 = 0xffa12360
     r8 = 0xffa122d8    r9 = 0xffa12300   r10 = 0xffa12240    fp = 0xffa12280
     sp = 0xffa12238    pc = 0x037caac3
    Found by: call frame info
20  chrome!base::MessagePumpLibevent::Run(base::MessagePump::Delegate*) [message_pump_libevent.cc : 210 + 0x7]
     r4 = 0x094f2e40    r5 = 0xffa12478    r6 = 0x0950d3c0    r7 = 0xffa123b0
     r8 = 0x094f2e48    r9 = 0xf7008ec0   r10 = 0xffa12388    fp = 0x00000000
     sp = 0xffa12368    pc = 0x037cf2f3
    Found by: call frame info
21  chrome!base::time_internal::TimeBase<base::TimeTicks>::TimeBase(long long) [run_loop.cc : 102 + 0x5]
     r4 = 0xffa123cc    r5 = 0x00000000    r6 = 0x00000007    r7 = 0xffa123c0
     r8 = 0xf7008ec0    r9 = 0x09485780   r10 = 0x00000000    fp = 0x00000000
     sp = 0xffa123b8    pc = 0x050aed2b
    Found by: call frame info
22  chrome!content::UtilityMain(content::MainFunctionParams const&) [utility_main.cc : 103 + 0x3]
     r4 = 0xffa123cc    r5 = 0x00000000    r6 = 0x00000007    r7 = 0xffa12538
     r8 = 0xf7008ec0    r9 = 0x09485780   r10 = 0x00000000    fp = 0x00000000
     sp = 0xffa123c8    pc = 0x04e6be0f

It looks like immersive_fullscreen_controller_ is null here:
https://cs.chromium.org/chromium/src/ash/frame/custom_frame_view_ash.cc?type=cs&q=CustomFrameViewAshWindowStateDelegate::OnPostWindowStateTypeChange&sq=package:chromium&g=0&l=143

It might be related to this:
https://chromium-review.googlesource.com/c/chromium/src/+/987542

I'm not sure what the semantics are around "enable_immersive" in this class.

I'm also not sure why it happens on scarlet -- maybe that machine always comes up in tablet mode?