Chrome Version: (copy from chrome://version)

Chromium	58.0.2999.0 (Developer Build) (64-bit)
Revision	7f6a27f1dbe4d8cafffb919445bc93bb8867a8fe-refs/heads/master@{#447346}
OS	Linux
JavaScript	V8 5.8.86
Flash	(Disabled)
User Agent	Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.2999.0 Safari/537.36
Command Line	out/Default/chrome --flag-switches-begin --flag-switches-end
Executable Path	/usr/local/google/home/csashi/linux_chromium/src/out/Default/chrome
Profile Path	/usr/local/google/home/csashi/.config/chromium/Default
Variations	AutofillFieldMetadata:Enabled
AutofillProfileOrderByFrecency:EnabledLimitTo3
BrowserScheduler:Default
CSSExternalScanner:Enabled_ScanAndPreload
DataReductionProxyUseQuic:Enabled
DisallowFetchForDocWrittenScriptsInMainFrame:DocumentWriteEvaluatorGroup
EnableSyncUSSDeviceInfo:Enabled
ExpensiveBackgroundTimerThrottling:Enabled_30sMaxThrottilingDelay
ExtensionActionRedesign:Enabled
FasterLocationReload:Enabled
Html5ByDefault:Enabled
HttpFormWarning:Enabled
InstanceID:Enabled
NetDelayableH2AndQuicRequests:Enabled
NetProxyPreconnects:NetProxyPreconnects
NetworkTimeQueries:NetworkTimeQueriesEnabledBackgroundAndOnDemand
OfferUploadCreditCards:Enabled
PageRevisitInstrumentation:Enabled
ParseHTMLOnMainThread:Enabled
PassiveDocumentEventListeners:Enabled
PassiveEventListenersDueToFling:Enabled
PasswordManagerSettingsMigration:Enable
PersistentHistograms:EnabledInMemory
PointerEvent:Enabled
PreconnectMore:Enabled
QUIC:Enabled
RafAlignedMouseInput:Enabled
RafAlignedTouchInput:Enabled
SafeBrowsingIncidentReportingService:Enabled
SafeBrowsingScoutTransitionStudy:CanShowScoutOptInGroup
SimpleCacheTrial:ExperimentYes
SpeculativeLaunchServiceWorker:Enabled
TLS13Negotiation:Enabled
TokenBinding:TokenBinding
TranslateRanker:EnforcementEnabled
V8CacheStrategiesForCacheStorage:default
WebFontsInterventionV2:Enabled‑slow2g

OS: Linux (Ubuntu)

What steps will reproduce the problem?
(1) Install Chrome Vox
(2) Visit dump-truck.appspot.com
(3) Close browser

What is the expected result?
Browser should close cleanly.

What happens instead?
[28510:28510:0202/145704.811197:FATAL:observer_list.h(276)] Check failed: false. Observers can only be added once!
#0 0x7f45749e3b9b base::debug::StackTrace::StackTrace()
#1 0x7f45749e21dc base::debug::StackTrace::StackTrace()
#2 0x7f4574a4ff6f logging::LogMessage::~LogMessage()
#3 0x7f4567e4271e base::ObserverListBase<>::AddObserver()
#4 0x7f4567e3e920 aura::Window::AddObserver()
#5 0x7f4569b1fa36 views::AXAuraObjCache::GetOrCreate()
#6 0x7f4569b2bb7b views::AXWindowObjWrapper::GetChildren()
#7 0x7f45796f9edb AXTreeSourceAura::GetChildren()
#8 0x7f45796f3787 ui::AXTreeSerializer<>::AnyDescendantWasReparented()
#9 0x7f45796f1429 ui::AXTreeSerializer<>::SerializeChanges()
#10 0x7f45796f01a8 AutomationManagerAura::SendEvent()
#11 0x7f45796f096d AutomationManagerAura::OnChildWindowRemoved()
#12 0x7f4569b1fd21 views::AXAuraObjCache::Remove()
#13 0x7f4569b2be3a views::AXWindowObjWrapper::OnWindowHierarchyChanged()
#14 0x7f4567e4077f aura::Window::NotifyWindowHierarchyChangeAtReceiver()
#15 0x7f4567e4049b aura::Window::NotifyWindowHierarchyChangeDown()
#16 0x7f4567e3dcbc aura::Window::NotifyWindowHierarchyChange()
#17 0x7f4567e3b2db aura::Window::RemoveChild()
#18 0x7f4567e3ac32 aura::Window::~Window()
#19 0x7f4567e3b3b9 aura::Window::~Window()
#20 0x7f4567ce79e6 wm::TransientWindowManager::OnWindowDestroying()
#21 0x7f4567e3aaf0 aura::Window::~Window()
#22 0x7f4567e3b3b9 aura::Window::~Window()
#23 0x7f4567e3b0c1 aura::Window::RemoveOrDestroyChildren()
#24 0x7f4567e3ac07 aura::Window::~Window()
#25 0x7f4567e3b3b9 aura::Window::~Window()
#26 0x7f4567e3b0c1 aura::Window::RemoveOrDestroyChildren()
#27 0x7f4567e3ac07 aura::Window::~Window()
#28 0x7f4567e3b3b9 aura::Window::~Window()
#29 0x7f4567e53583 aura::WindowTreeHost::DestroyDispatcher()
#30 0x7f4569b6d6e2 views::DesktopWindowTreeHostX11::~DesktopWindowTreeHostX11()
#31 0x7f45797b9ccb BrowserDesktopWindowTreeHostX11::~BrowserDesktopWindowTreeHostX11()
#32 0x7f45797b9d79 BrowserDesktopWindowTreeHostX11::~BrowserDesktopWindowTreeHostX11()
#33 0x7f45699b385f std::default_delete<>::operator()()
#34 0x7f4569b4b49c std::unique_ptr<>::reset()
#35 0x7f4569b45e2c views::DesktopNativeWidgetAura::OnHostClosed()
#36 0x7f45797b92a0 DesktopBrowserFrameAura::OnHostClosed()
#37 0x7f4569b6fcd4 views::DesktopWindowTreeHostX11::CloseNow()
#38 0x7f45797b9f6a BrowserDesktopWindowTreeHostX11::CloseNow()
#39 0x7f4569acb2e7 _ZN4base8internal13FunctorTraitsIMN5views12MouseWatcher8ObserverEFvvEvE6InvokeIRKNS_7WeakPtrIS4_EEJEEEvS6_OT_DpOT0_
#40 0x7f4569b80e2a _ZN4base8internal12InvokeHelperILb1EvE8MakeItSoIRKMN5views24DesktopWindowTreeHostX11EFvvERKNS_7WeakPtrIS5_EEJEEEvOT_OT0_DpOT1_
#41 0x7f4569b80db2 _ZN4base8internal7InvokerINS0_9BindStateIMN5views24DesktopWindowTreeHostX11EFvvEJNS_7WeakPtrIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#42 0x7f4569b80cfc _ZN4base8internal7InvokerINS0_9BindStateIMN5views24DesktopWindowTreeHostX11EFvvEJNS_7WeakPtrIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#43 0x7f45749e9971 _ZNO4base8internal8RunMixinINS_8CallbackIFvvELNS0_8CopyModeE0ELNS0_10RepeatModeE0EEEE3RunEv
#44 0x7f45749e9362 base::debug::TaskAnnotator::RunTask()
#45 0x7f4574a747af base::MessageLoop::RunTask()
#46 0x7f4574a74a34 base::MessageLoop::DeferOrRunPendingTask()
#47 0x7f4574a74d1e base::MessageLoop::DoWork()
#48 0x7f4574a8cbac base::MessagePumpGlib::HandleDispatch()
#49 0x7f4574a8d351 base::(anonymous namespace)::WorkSourceDispatch()
#50 0x7f456388fe04 g_main_context_dispatch
#51 0x7f4563890048 <unknown>
#52 0x7f45638900ec g_main_context_iteration
#53 0x7f4574a8ccaf base::MessagePumpGlib::Run()
#54 0x7f4574a74357 base::MessageLoop::RunHandler()
#55 0x7f4574b1789a base::RunLoop::Run()
#56 0x7f457733f4fe ChromeBrowserMainParts::MainMessageLoopRun()
#57 0x7f456de0fb68 content::BrowserMainLoop::RunMainMessageLoopParts()
#58 0x7f456de1e7b6 content::BrowserMainRunnerImpl::Run()
#59 0x7f456de08fd8 content::BrowserMain()
#60 0x7f456f5d9046 content::RunNamedProcessTypeMain()
#61 0x7f456f5db45c content::ContentMainRunnerImpl::Run()