Chrome Version: 67.0.3381.0
OS: Windows 10

What steps will reproduce the problem?
[(0) Run a Chrome build with DCHECKs enabled.]
(1) Start downloading a large file over HTTP.
(2) Close the browser.
(3) When prompted, choose to "Continue downloading".

What is the expected result?

Expect that the browser continues downloading.

What happens instead?

Browser crashes with a DCHECK on |is_attempting_to_close_browser_| in UnloadController::CancelWindowClose():

[72116:108588:0329/173026.858:FATAL:unload_controller.cc(209)] Check failed: is_attempting_to_close_browser_.
Backtrace:
        base::debug::StackTrace::StackTrace [0x00007FFFA579CD25+101] (C:\src\git-chrome\src\base\debug\stack_trace_win.cc:286)
        base::debug::StackTrace::StackTrace [0x00007FFFA579B9CF+31] (C:\src\git-chrome\src\base\debug\stack_trace.cc:199)
        logging::LogMessage::~LogMessage [0x00007FFFA5813966+134] (C:\src\git-chrome\src\base\logging.cc:595)
        UnloadController::CancelWindowClose [0x00007FFF9A4647BD+189] (C:\src\git-chrome\src\chrome\browser\ui\unload_controller.cc:210)
        Browser::InProgressDownloadResponse [0x00007FFF99F0A046+166] (C:\src\git-chrome\src\chrome\browser\ui\browser.cc:801)
        base::internal::FunctorTraits<void (Browser::*)(bool),void>::Invoke<const base::WeakPtr<Browser> &,bool> [0x00007FFF99F22A07+103] (C:\src\git-chrome\src\base\bind_internal.h:447)
        base::internal::InvokeHelper<1,void>::MakeItSo<void (Browser::*const &)(bool),const base::WeakPtr<Browser> &,bool> [0x00007FFF99F22914+132] (C:\src\git-chrome\src\base\bind_internal.h:553)
        base::internal::Invoker<base::internal::BindState<void (Browser::*)(bool),base::WeakPtr<Browser> >,void (bool)>::RunImpl<void (Browser::*const &)(bool),const std::tuple<base::WeakPtr<Browser> > &,0> [0x00007FFF99F22864+100] (C:\src\git-chrome\src\base\bind_internal.h:604)
        base::internal::Invoker<base::internal::BindState<void (Browser::*)(bool),base::WeakPtr<Browser> >,void (bool)>::Run [0x00007FFF99F22731+97] (C:\src\git-chrome\src\base\bind_internal.h:586)
        base::RepeatingCallback<void (bool)>::Run [0x00007FFF9596B4FB+123] (C:\src\git-chrome\src\base\callback.h:124)
        DownloadInProgressDialogView::Cancel [0x00007FFF9A7C11EC+28] (C:\src\git-chrome\src\chrome\browser\ui\views\download\download_in_progress_dialog_view.cc:81)
        views::DialogClientView::CancelWindow [0x00007FFF940BD0ED+61] (C:\src\git-chrome\src\ui\views\window\dialog_client_view.cc:101)
        views::DialogClientView::ButtonPressed [0x00007FFF940BDE26+166] (C:\src\git-chrome\src\ui\views\window\dialog_client_view.cc:240)
        views::Button::NotifyClick [0x00007FFF93F26BE3+131] (C:\src\git-chrome\src\ui\views\controls\button\button.cc:496)
        views::Button::OnMouseReleased [0x00007FFF93F256AC+236] (C:\src\git-chrome\src\ui\views\controls\button\button.cc:234)
        views::View::ProcessMouseReleased [0x00007FFF9407A6B8+248] (C:\src\git-chrome\src\ui\views\view.cc:2585)
        views::View::OnMouseEvent [0x00007FFF94079CC7+279] (C:\src\git-chrome\src\ui\views\view.cc:1109)
        views::InkDropHostView::OnMouseEvent [0x00007FFF93EE5C75+357] (C:\src\git-chrome\src\ui\views\animation\ink_drop_host_view.cc:277)
        ui::EventHandler::OnEvent [0x00007FFFA281AB52+146] (C:\src\git-chrome\src\ui\events\event_handler.cc:27)
        ui::ScopedTargetHandler::OnEvent [0x00007FFFA2832CDE+94] (C:\src\git-chrome\src\ui\events\scoped_target_handler.cc:34)
        ui::EventDispatcher::DispatchEvent [0x00007FFFA2817739+185] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:192)
        ui::EventDispatcher::ProcessEvent [0x00007FFFA28167DD+397] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:140)
        ui::EventDispatcherDelegate::DispatchEventToTarget [0x00007FFFA28163FF+127] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:87)
        ui::EventDispatcherDelegate::DispatchEvent [0x00007FFFA28161D7+375] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:58)
        views::internal::RootView::OnMouseReleased [0x00007FFF94099DAF+255] (C:\src\git-chrome\src\ui\views\widget\root_view.cc:443)
        views::Widget::OnMouseEvent [0x00007FFF940A6933+723] (C:\src\git-chrome\src\ui\views\widget\widget.cc:1221)
        views::DesktopNativeWidgetAura::OnMouseEvent [0x00007FFF941650ED+333] (C:\src\git-chrome\src\ui\views\widget\desktop_aura\desktop_native_widget_aura.cc:1053)
        ui::EventHandler::OnEvent [0x00007FFFA281AB52+146] (C:\src\git-chrome\src\ui\events\event_handler.cc:27)
        ui::EventDispatcher::DispatchEvent [0x00007FFFA2817739+185] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:192)
        ui::EventDispatcher::ProcessEvent [0x00007FFFA28167DD+397] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:140)
        ui::EventDispatcherDelegate::DispatchEventToTarget [0x00007FFFA28163FF+127] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:87)
        ui::EventDispatcherDelegate::DispatchEvent [0x00007FFFA28161D7+375] (C:\src\git-chrome\src\ui\events\event_dispatcher.cc:58)
        ui::EventProcessor::OnEventFromSource [0x00007FFFA281C34D+1341] (C:\src\git-chrome\src\ui\events\event_processor.cc:57)
        ui::EventSource::DeliverEventToSink [0x00007FFFA281E978+216] (C:\src\git-chrome\src\ui\events\event_source.cc:95)
        ui::EventSource::SendEventToSink [0x00007FFFA281DF0D+1293] (C:\src\git-chrome\src\ui\events\event_source.cc:74)
        views::DesktopWindowTreeHostWin::HandleMouseEvent [0x00007FFF94182D63+83] (C:\src\git-chrome\src\ui\views\widget\desktop_aura\desktop_window_tree_host_win.cc:863)
        views::HWNDMessageHandler::HandleMouseEventInternal [0x00007FFF940E08AF+1967] (C:\src\git-chrome\src\ui\views\win\hwnd_message_handler.cc:2747)
        views::HWNDMessageHandler::OnMouseRange [0x00007FFF940D26F7+55] (C:\src\git-chrome\src\ui\views\win\hwnd_message_handler.cc:1747)
        views::HWNDMessageHandler::_ProcessWindowMessage [0x00007FFF940CD5EC+268] (C:\src\git-chrome\src\ui\views\win\hwnd_message_handler.h:355)
        views::HWNDMessageHandler::OnWndProc [0x00007FFF940DF307+295] (C:\src\git-chrome\src\ui\views\win\hwnd_message_handler.cc:929)
        gfx::WindowImpl::WndProc [0x00007FFFBD71B7A0+384] (C:\src\git-chrome\src\ui\gfx\win\window_impl.cc:303)
        base::win::WrappedWindowProc<&gfx::WindowImpl::WndProc> [0x00007FFFBD71A5B5+53] (C:\src\git-chrome\src\base\win\wrapped_window_proc.h:76)
        CallWindowProcW [0x00007FFFF1AD1C24+1268]
        DispatchMessageW [0x00007FFFF1AD156C+444]
        base::MessagePumpForUI::ProcessMessageHelper [0x00007FFFA586CE38+888] (C:\src\git-chrome\src\base\message_loop\message_pump_win.cc:365)
        base::MessagePumpForUI::ProcessNextWindowsMessage [0x00007FFFA586C4C0+160] (C:\src\git-chrome\src\base\message_loop\message_pump_win.cc:339)
        base::MessagePumpForUI::DoRunLoop [0x00007FFFA586C23D+29] (C:\src\git-chrome\src\base\message_loop\message_pump_win.cc:169)
        base::MessagePumpWin::Run [0x00007FFFA586B427+199] (C:\src\git-chrome\src\base\message_loop\message_pump_win.cc:58)
        base::MessageLoop::Run [0x00007FFFA585DD80+576] (C:\src\git-chrome\src\base\message_loop\message_loop.cc:344)
        base::RunLoop::Run [0x00007FFFA596A44B+507] (C:\src\git-chrome\src\base\run_loop.cc:133)
        ChromeBrowserMainParts::MainMessageLoopRun [0x00007FFF979F486A+362] (C:\src\git-chrome\src\chrome\browser\chrome_browser_main.cc:2172)
        content::BrowserMainLoop::RunMainMessageLoopParts [0x00007FFF8D66A3C1+481] (C:\src\git-chrome\src\content\browser\browser_main_loop.cc:1053)
        content::BrowserMainRunnerImpl::Run [0x00007FFF8D67D6FF+335] (C:\src\git-chrome\src\content\browser\browser_main_runner.cc:162)
        content::BrowserMain [0x00007FFF8D65FB43+259] (C:\src\git-chrome\src\content\browser\browser_main.cc:46)
        content::RunNamedProcessTypeMain [0x00007FFF9097115C+220] (C:\src\git-chrome\src\content\app\content_main_runner.cc:423)
        content::ContentMainRunnerImpl::Run [0x00007FFF90971F54+580] (C:\src\git-chrome\src\content\app\content_main_runner.cc:704)
        content::ContentServiceManagerMainDelegate::RunEmbedderProcess [0x00007FFF9096CF1A+42] (C:\src\git-chrome\src\content\app\content_service_manager_main_delegate.cc:51)
        service_manager::Main [0x00007FFF77177B66+1302] (C:\src\git-chrome\src\services\service_manager\embedder\main.cc:453)
        content::ContentMain [0x00007FFF90970FBF+95] (C:\src\git-chrome\src\content\app\content_main.cc:20)
        ChromeMain [0x00007FFF94DFEF23+435] (C:\src\git-chrome\src\chrome\app\chrome_main.cc:101)
        MainDllLoader::Launch [0x00007FF6EEDE2F84+1124] (C:\src\git-chrome\src\chrome\app\main_dll_loader_win.cc:198)
        wWinMain [0x00007FF6EEDD5D50+1136] (C:\src\git-chrome\src\chrome\app\chrome_exe_main_win.cc:230)