The failure occurs when opening the dialog from the in-page Cast button on YouTube. It doesn't happen if opened on another site or via another method.
There doesn't seem to be a user-noticeable issue associated with the failure.

[245010:245010:1207/135328.680325:FATAL:view.cc(188)] Check failed: !iterating_. 
#0 0x7fe3c277d06f base::debug::StackTrace::StackTrace()
#1 0x7fe3c26a11eb logging::LogMessage::~LogMessage()
#2 0x7fe3bccf0148 views::View::AddChildViewAt()
#3 0x7fe3bccb4fae views::ScrollView::UpdateOverflowIndicatorVisibility()
#4 0x7fe3bccb588e views::ScrollView::ScrollToOffset()
#5 0x7fe3bccb5cde views::ScrollView::ScrollContentsRegionToBeVisible()
#6 0x7fe3bccb5fa5 views::ScrollView::Viewport::ScrollRectToVisible()
#7 0x7fe3bccf7f27 views::View::ScrollRectToVisible()
#8 0x7fe3bccf7f27 views::View::ScrollRectToVisible()
#9 0x7fe3bccf7f58 views::View::ScrollViewToVisible()
#10 0x7fe3bccf9eea views::View::Focus()
#11 0x7fe3bcce079d views::FocusManager::SetFocusedViewWithReason()
#12 0x7fe3bcce12dc views::FocusManager::RestoreFocusedView()
#13 0x7fe3bcd23f39 views::NativeWidgetAura::OnWindowActivated()
#14 0x7fe3bc18e1c6 wm::FocusController::SetActiveWindow()
#15 0x7fe3bc18cb58 wm::FocusController::FocusAndActivateWindow()
#16 0x7fe3bcd22a14 views::NativeWidgetAura::Activate()
#17 0x7fe3bcce05fa views::FocusManager::SetFocusedViewWithReason()
#18 0x7fe3bcc82f77 views::Button::SetState()
#19 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#20 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#21 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#22 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#23 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#24 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#25 0x7fe3bccf373e views::View::PropagateVisibilityNotifications()
#26 0x7fe3bcd03d62 views::Widget::OnNativeWidgetVisibilityChanged()
#27 0x7fe3bdb17860 aura::Window::SetVisible()
#28 0x7fe3bdb17599 aura::Window::Show()
#29 0x7fe3bcd228bd views::NativeWidgetAura::Show()
#30 0x7fe3bcd02d8e views::Widget::Show()
#31 0x556c55d69d0b media_router::CastDialogView::ShowDialog()
#32 0x556c55d69bd7 media_router::CastDialogView::ShowDialogWithToolbarAction()
#33 0x556c55d698c0 media_router::MediaRouterDialogControllerViews::CreateMediaRouterDialog()
#34 0x556c5566f1c8 media_router::MediaRouterDialogController::ShowMediaRouterDialogForPresentation()
#35 0x556c5566b04c media_router::PresentationServiceDelegateImpl::StartPresentation()