ToT r510545 on linux desktop

I was running --mash --force-tablet-mode=touch_view to get into tablet mode on startup. I hit this:

[164545:164545:1020/142354.228611:FATAL:custom_frame_view_ash.cc(136)] Check failed: immersive_fullscreen_controller_. 
#0 0x7fc7a99bb6ac base::debug::StackTrace::StackTrace()
#1 0x7fc7a99e1d1c logging::LogMessage::~LogMessage()
#2 0x7fc7a42b6261 ash::(anonymous namespace)::CustomFrameViewAshWindowStateDelegate::OnPostWindowStateTypeChange()
#3 0x7fc7a43f7457 ash::wm::WindowState::NotifyPostStateTypeChange()
#4 0x7fc7a43bee0b ash::wm::DefaultState::EnterToNextState()
#5 0x7fc7a43be475 ash::wm::DefaultState::OnWMEvent()
#6 0x7fc7a43f7b85 ash::wm::WindowState::OnWindowPropertyChanged()
#7 0x7fc7a56571ca aura::Window::AfterPropertyChange()
#8 0x7fc7a9dca108 ui::PropertyHandler::SetPropertyInternal()
#9 0x7fc7a563da10 aura::PropertyConverter::SetPropertyFromTransportValue()
#10 0x7fc7a564cc0f aura::WindowTreeClient::WmSetProperty()
#11 0x7fc7a566b8ab ui::mojom::WindowManagerStubDispatch::Accept()
#12 0x7fc7a8c7725b mojo::InterfaceEndpointClient::HandleValidatedMessage()
#13 0x7fc7a8c76ba6 mojo::FilterChain::Accept()

Code is here:

  // wm::WindowStateObserver:
  void OnPostWindowStateTypeChange(wm::WindowState* window_state,
                                   mojom::WindowStateType old_type) override {
    if (Shell::Get()->tablet_mode_controller() &&
        Shell::Get()->tablet_mode_controller()->ShouldAutoHideTitlebars()) {
      DCHECK(immersive_fullscreen_controller_);

I'm not sure if this is a normal startup path on actual devices, but it's a bit concerning.