Add CHECK to WidgetObserver subclasses

WidgetObservers need to be removed from all ObserverLists before
destruction otherwise it will CHECK fail when iterating over the list.
The CHECK is added to all subclasses to retain readable stack traces in
release builds.

The goal is to find all instances where the observer is not removed as
that causes a hard to reproduce failure.

AX-Relnotes: n/a.
Bug: 1055483
Change-Id: I481ee30e681220ff697c7fbb2380470f17cfd465
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254598Reviewed-by: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Richard Knoll <knollr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781737}

ash/accessibility/focus_ring_controller.cc

@@ -19,6 +19,7 @@ FocusRingController::FocusRingController() : visible_(false), widget_(NULL) {}
 
 FocusRingController::~FocusRingController() {
   SetVisible(false);
+  CHECK(!IsInObserverList());
 }
 
 void FocusRingController::SetVisible(bool visible) {

ash/app_list/app_list_presenter_impl.cc

@@ -107,6 +107,7 @@ AppListPresenterImpl::~AppListPresenterImpl() {
     if (view_->GetWidget())
       view_->GetWidget()->CloseNow();
   }
+  CHECK(!IsInObserverList());
 }
 
 aura::Window* AppListPresenterImpl::GetWindow() const {

ash/assistant/assistant_web_ui_controller.cc

@@ -71,6 +71,7 @@ AssistantWebUiController::AssistantWebUiController() {
 
 AssistantWebUiController::~AssistantWebUiController() {
   CloseUi();
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void AssistantWebUiController::OnWidgetDestroying(views::Widget* widget) {

ash/ime/mode_indicator_observer.cc

@@ -13,6 +13,7 @@ ModeIndicatorObserver::ModeIndicatorObserver() : active_widget_(nullptr) {}
 ModeIndicatorObserver::~ModeIndicatorObserver() {
   if (active_widget_)
     active_widget_->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void ModeIndicatorObserver::AddModeIndicatorWidget(views::Widget* widget) {

ash/magnifier/docked_magnifier_controller_impl.cc

@@ -115,6 +115,7 @@ DockedMagnifierControllerImpl::~DockedMagnifierControllerImpl() {
     shell->window_tree_host_manager()->RemoveObserver(this);
     shell->RemovePreTargetHandler(this);
   }
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 // static

ash/magnifier/magnifier_glass.cc

@@ -184,6 +184,7 @@ MagnifierGlass::MagnifierGlass(Params params) : params_(std::move(params)) {}
 
 MagnifierGlass::~MagnifierGlass() {
   CloseMagnifierWindow();
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void MagnifierGlass::ShowFor(aura::Window* root_window,

ash/public/cpp/external_arc/message_center/arc_notification_content_view.cc

@@ -291,6 +291,7 @@ ArcNotificationContentView::~ArcNotificationContentView() {
     item_->RemoveObserver(this);
     item_->DecrementWindowRefCount();
   }
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 const char* ArcNotificationContentView::GetClassName() const {

ash/shelf/login_shelf_gesture_controller.cc

@@ -118,6 +118,7 @@ LoginShelfGestureController::~LoginShelfGestureController() {
   nudge_ = nullptr;
 
   std::move(exit_handler_).Run();
+  CHECK(!IsInObserverList());
 }
 
 bool LoginShelfGestureController::HandleGestureEvent(

ash/system/message_center/ash_message_popup_collection.cc

@@ -49,6 +49,7 @@ AshMessagePopupCollection::~AshMessagePopupCollection() {
   shelf_->RemoveObserver(this);
   for (views::Widget* widget : tracked_widgets_)
     widget->RemoveObserver(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void AshMessagePopupCollection::StartObserving(

ash/system/message_center/unified_message_center_bubble.cc

@@ -132,6 +132,7 @@ UnifiedMessageCenterBubble::~UnifiedMessageCenterBubble() {
     bubble_widget_->RemoveObserver(this);
     bubble_widget_->CloseNow();
   }
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 int UnifiedMessageCenterBubble::CalculateAvailableHeight() {

ash/system/palette/palette_welcome_bubble.cc

@@ -81,6 +81,7 @@ PaletteWelcomeBubble::~PaletteWelcomeBubble() {
     Shell::Get()->RemovePreTargetHandler(this);
   }
   Shell::Get()->session_controller()->RemoveObserver(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 // static

ash/system/tray/tray_bubble_wrapper.cc

@@ -48,6 +48,7 @@ TrayBubbleWrapper::~TrayBubbleWrapper() {
     bubble_widget_->RemoveObserver(this);
     bubble_widget_->Close();
   }
+  CHECK(!IsInObserverList());
 }
 
 TrayBackgroundView* TrayBubbleWrapper::GetTray() const {

ash/system/unified/unified_system_tray_bubble.cc

@@ -128,6 +128,7 @@ UnifiedSystemTrayBubble::~UnifiedSystemTrayBubble() {
     bubble_widget_->RemoveObserver(this);
     bubble_widget_->Close();
   }
+  CHECK(!IsInObserverList());
 }
 
 gfx::Rect UnifiedSystemTrayBubble::GetBoundsInScreen() const {

ash/touch/touch_hud_renderer.cc

@@ -131,6 +131,7 @@ TouchHudRenderer::TouchHudRenderer(views::Widget* parent_widget)
 TouchHudRenderer::~TouchHudRenderer() {
   if (parent_widget_)
     parent_widget_->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void TouchHudRenderer::Clear() {

ash/touch/touch_observer_hud.cc

@@ -59,6 +59,7 @@ TouchObserverHud::~TouchObserverHud() {
   display::Screen::GetScreen()->RemoveObserver(this);
 
   widget_->RemoveObserver(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void TouchObserverHud::Remove() {

chrome/browser/chromeos/accessibility/accessibility_manager.cc

@@ -164,7 +164,7 @@ class AccessibilityPanelWidgetObserver : public views::WidgetObserver {
     widget_->AddObserver(this);
   }
 
-  ~AccessibilityPanelWidgetObserver() override = default;
+  ~AccessibilityPanelWidgetObserver() override { CHECK(!IsInObserverList()); }
 
   void OnWidgetClosing(views::Widget* widget) override {
     CHECK_EQ(widget_, widget);

chrome/browser/chromeos/crostini/crostini_force_close_watcher.cc

@@ -56,7 +56,9 @@ ForceCloseWatcher::ForceCloseWatcher(std::unique_ptr<Delegate> delegate)
   delegate_->Watched(this);
 }
 
-ForceCloseWatcher::~ForceCloseWatcher() = default;
+ForceCloseWatcher::~ForceCloseWatcher() {
+  CHECK(!IsInObserverList());
+}
 
 ShellSurfaceForceCloseDelegate::ShellSurfaceForceCloseDelegate(
     exo::ShellSurfaceBase* shell_surface,
@@ -69,7 +71,9 @@ void ShellSurfaceForceCloseDelegate::ForceClose() {
   GetClosableWidget()->CloseNow();
 }
 
-ShellSurfaceForceCloseDelegate::~ShellSurfaceForceCloseDelegate() = default;
+ShellSurfaceForceCloseDelegate::~ShellSurfaceForceCloseDelegate() {
+  CHECK(!IsInObserverList());
+}
 
 views::Widget* ShellSurfaceForceCloseDelegate::GetClosableWidget() {
   DCHECK(shell_surface_->GetWidget());

chrome/browser/chromeos/input_method/assistive_window_controller.cc

@@ -90,6 +90,7 @@ AssistiveWindowController::~AssistiveWindowController() {
     suggestion_window_view_->GetWidget()->RemoveObserver(this);
   if (undo_window_ && undo_window_->GetWidget())
     undo_window_->GetWidget()->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void AssistiveWindowController::InitSuggestionWindow() {

chrome/browser/chromeos/input_method/candidate_window_controller_impl.cc

@@ -32,6 +32,7 @@ CandidateWindowControllerImpl::~CandidateWindowControllerImpl() {
     candidate_window_view_->RemoveObserver(this);
     candidate_window_view_->GetWidget()->RemoveObserver(this);
   }
+  CHECK(!IsInObserverList());
 }
 
 void CandidateWindowControllerImpl::InitCandidateWindowView() {

chrome/browser/chromeos/lock_screen_apps/first_app_run_toast_manager.cc

@@ -42,6 +42,7 @@ class FirstAppRunToastManager::AppWidgetObserver
   ~AppWidgetObserver() override {
     // This is a no-op of the observer was previously removed.
     widget_->RemoveObserver(this);
+    CHECK(!IsInObserverList());
   }
 
   // views::WidgetObserver:

chrome/browser/chromeos/login/ui/captive_portal_window_proxy.cc

@@ -70,11 +70,12 @@ CaptivePortalWindowProxy::CaptivePortalWindowProxy(
 }
 
 CaptivePortalWindowProxy::~CaptivePortalWindowProxy() {
-  if (!widget_)
-    return;
-  DCHECK_EQ(STATE_DISPLAYED, GetState());
-  widget_->RemoveObserver(this);
-  widget_->Close();
+  if (widget_) {
+    DCHECK_EQ(STATE_DISPLAYED, GetState());
+    widget_->RemoveObserver(this);
+    widget_->Close();
+  }
+  CHECK(!IsInObserverList());
 }
 
 void CaptivePortalWindowProxy::ShowIfRedirected() {

chrome/browser/chromeos/login/ui/login_display_host_webui.cc

@@ -368,6 +368,7 @@ class CloseAfterCommit : public ui::CompositorObserver,
   ~CloseAfterCommit() override {
     widget_->RemoveObserver(this);
     widget_->GetCompositor()->RemoveObserver(this);
+    CHECK(!IsInObserverList());
   }
 
   // ui::CompositorObserver:
@@ -487,6 +488,7 @@ LoginDisplayHostWebUI::~LoginDisplayHostWebUI() {
     (new DriveFirstRunController(ProfileManager::GetActiveUserProfile()))
         ->EnableOfflineMode();
   }
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 ////////////////////////////////////////////////////////////////////////////////

chrome/browser/chromeos/power/idle_action_warning_observer.cc

@@ -52,6 +52,7 @@ IdleActionWarningObserver::~IdleActionWarningObserver() {
     warning_dialog_->GetWidget()->RemoveObserver(this);
     warning_dialog_->CloseDialog();
   }
+  CHECK(!IsInObserverList());
 }
 
 void IdleActionWarningObserver::IdleActionImminent(

chrome/browser/ui/ash/keyboard/chrome_keyboard_bounds_observer.cc

@@ -58,6 +58,7 @@ ChromeKeyboardBoundsObserver::~ChromeKeyboardBoundsObserver() {
   RemoveAllObservedWindows();
 
   ChromeKeyboardControllerClient::Get()->RemoveObserver(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void ChromeKeyboardBoundsObserver::OnKeyboardOccludedBoundsChanged(

chrome/browser/ui/ash/launcher/extension_app_window_launcher_controller.cc

@@ -62,6 +62,7 @@ ExtensionAppWindowLauncherController::~ExtensionAppWindowLauncherController() {
     DCHECK(widget);  // Extension windows are always backed by Widgets.
     widget->RemoveObserver(this);
   }
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 AppWindowLauncherItemController*

chrome/browser/ui/views/autofill/autofill_popup_base_view.cc

@@ -82,6 +82,8 @@ AutofillPopupBaseView::~AutofillPopupBaseView() {
 
     RemoveWidgetObservers();
   }
+
+  CHECK(!IsInObserverList());
 }
 
 void AutofillPopupBaseView::DoShow() {

chrome/browser/ui/views/exclusive_access_bubble_views.cc

@@ -102,6 +102,7 @@ ExclusiveAccessBubbleViews::~ExclusiveAccessBubbleViews() {
   // itself.
   popup_->Close();
   base::ThreadTaskRunnerHandle::Get()->DeleteSoon(FROM_HERE, popup_);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void ExclusiveAccessBubbleViews::UpdateContent(

chrome/browser/ui/views/extensions/extensions_toolbar_button.cc

@@ -39,7 +39,9 @@ ExtensionsToolbarButton::ExtensionsToolbarButton(
   GetViewAccessibility().OverrideHasPopup(ax::mojom::HasPopup::kMenu);
 }
 
-ExtensionsToolbarButton::~ExtensionsToolbarButton() = default;
+ExtensionsToolbarButton::~ExtensionsToolbarButton() {
+  CHECK(!IsInObserverList());
+}
 
 void ExtensionsToolbarButton::UpdateIcon() {
   SetImage(views::Button::STATE_NORMAL,

chrome/browser/ui/views/extensions/extensions_toolbar_container.cc

@@ -102,6 +102,7 @@ ExtensionsToolbarContainer::~ExtensionsToolbarContainer() {
   // The widgets should close synchronously (resulting in OnWidgetClosing()),
   // so |anchored_widgets_| should now be empty.
   DCHECK(anchored_widgets_.empty());
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void ExtensionsToolbarContainer::UpdateAllIcons() {

chrome/browser/ui/views/frame/immersive_mode_controller_mac.mm

@@ -225,7 +225,9 @@ ImmersiveModeControllerMac::RevealedLock::~RevealedLock() {
 ImmersiveModeControllerMac::ImmersiveModeControllerMac()
     : weak_ptr_factory_(this) {}
 
-ImmersiveModeControllerMac::~ImmersiveModeControllerMac() = default;
+ImmersiveModeControllerMac::~ImmersiveModeControllerMac() {
+  CHECK(!views::WidgetObserver::IsInObserverList());
+}
 
 void ImmersiveModeControllerMac::Init(BrowserView* browser_view) {
   browser_view_ = browser_view;

chrome/browser/ui/views/location_bar/permission_chip.cc

@@ -108,6 +108,7 @@ PermissionChip::PermissionChip(Browser* browser)
 PermissionChip::~PermissionChip() {
   if (prompt_bubble_)
     prompt_bubble_->GetWidget()->Close();
+  CHECK(!IsInObserverList());
 }
 
 void PermissionChip::Show(permissions::PermissionPrompt::Delegate* delegate) {

chrome/browser/ui/views/media_router/web_contents_display_observer_view.cc

@@ -41,6 +41,7 @@ WebContentsDisplayObserverView::~WebContentsDisplayObserverView() {
   if (widget_)
     widget_->RemoveObserver(this);
   BrowserList::RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void WebContentsDisplayObserverView::OnBrowserSetLastActive(Browser* browser) {

chrome/browser/ui/views/message_box_dialog.cc

@@ -254,6 +254,7 @@ MessageBoxDialog::MessageBoxDialog(const base::string16& title,
 
 MessageBoxDialog::~MessageBoxDialog() {
   GetWidget()->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void MessageBoxDialog::Run(MessageBoxResultCallback result_callback) {

chrome/browser/ui/views/omnibox/omnibox_popup_contents_view.cc

@@ -168,6 +168,7 @@ OmniboxPopupContentsView::~OmniboxPopupContentsView() {
   // closed the window, in which case it's been deleted, or it will soon.
   if (popup_)
     popup_->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void OmniboxPopupContentsView::OpenMatch(

chrome/browser/ui/views/permission_bubble/permission_prompt_impl.cc

@@ -83,6 +83,7 @@ PermissionPromptImpl::~PermissionPromptImpl() {
   if (prompt_style_ == PromptStyle::kChip && permission_chip_) {
     permission_chip_->Hide();
   }
+  CHECK(!IsInObserverList());
 }
 
 void PermissionPromptImpl::UpdateAnchorPosition() {

chrome/browser/ui/views/policy/enterprise_startup_dialog_view.cc

@@ -252,6 +252,7 @@ EnterpriseStartupDialogImpl::~EnterpriseStartupDialogImpl() {
     dialog_view_->RemoveWidgetObserver(this);
     dialog_view_->CloseDialog();
   }
+  CHECK(!IsInObserverList());
 }
 
 void EnterpriseStartupDialogImpl::DisplayLaunchingInformationWithThrobber(

chrome/browser/ui/views/relaunch_notification/relaunch_notification_controller_platform_impl_desktop.cc

@@ -57,6 +57,7 @@ RelaunchNotificationControllerPlatformImpl::
   DCHECK(!widget_);
   if (on_visible_)
     BrowserList::RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void RelaunchNotificationControllerPlatformImpl::NotifyRelaunchRecommended(

chrome/browser/ui/views/tabs/tab_drag_controller.cc

@@ -421,6 +421,7 @@ TabDragController::~TabDragController() {
         attached_context_ ? attached_context_ : source_context_;
     capture_context->AsView()->GetWidget()->ReleaseCapture();
   }
+  CHECK(!IsInObserverList());
 }
 
 void TabDragController::Init(TabDragContext* source_context,

chrome/browser/ui/views/tabs/tab_group_header.cc

@@ -396,6 +396,7 @@ TabGroupHeader::EditorBubbleTracker::~EditorBubbleTracker() {
     widget_->RemoveObserver(this);
     widget_->CloseWithReason(views::Widget::ClosedReason::kUnspecified);
   }
+  CHECK(!IsInObserverList());
 }
 
 void TabGroupHeader::EditorBubbleTracker::Opened(views::Widget* bubble_widget) {

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -1015,6 +1015,8 @@ TabStrip::~TabStrip() {
   // The child tabs may call back to us from their destructors. Delete them so
   // that if they call back we aren't in a weird state.
   RemoveAllChildViews(true);
+
+  CHECK(!IsInObserverList());
 }
 
 void TabStrip::SetAvailableWidthCallback(

chrome/browser/ui/views/toolbar/browser_actions_container.cc

@@ -118,6 +118,7 @@ BrowserActionsContainer::~BrowserActionsContainer() {
   toolbar_actions_bar_->DeleteActions();
   // All views should be removed as part of ToolbarActionsBar::DeleteActions().
   DCHECK(toolbar_action_views_.empty());
+  CHECK(!IsInObserverList());
 }
 
 std::string BrowserActionsContainer::GetIdAt(size_t index) const {

chrome/browser/ui/views/try_chrome_dialog_win/try_chrome_dialog.cc

@@ -309,6 +309,8 @@ class TryChromeDialog::Context {
 
     static std::unique_ptr<TaskbarCalculator> Create(Location location);
 
+    ~TaskbarCalculator() override { CHECK(!IsInObserverList()); }
+
     // DialogCalculator:
     void AddBorderToContents(views::Widget* popup,
                              views::View* contents_view) override;
@@ -1001,6 +1003,7 @@ TryChromeDialog::TryChromeDialog(size_t group, Delegate* delegate)
 
 TryChromeDialog::~TryChromeDialog() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(my_sequence_checker_);
+  CHECK(!IsInObserverList());
 }
 
 void TryChromeDialog::ShowDialogAsync() {

chromecast/graphics/accessibility/focus_ring_controller.cc

@@ -29,6 +29,7 @@ FocusRingController::FocusRingController(
 
 FocusRingController::~FocusRingController() {
   SetVisible(false);
+  CHECK(!IsInObserverList());
 }
 
 void FocusRingController::SetVisible(bool visible) {

chromecast/graphics/accessibility/partial_magnification_controller.cc

@@ -202,6 +202,7 @@ PartialMagnificationController::PartialMagnificationController(
 PartialMagnificationController::~PartialMagnificationController() {
   CloseMagnifierWindow();
   root_window_->RemovePreTargetHandler(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void PartialMagnificationController::SetEnabled(bool enabled) {

components/constrained_window/constrained_window_views.cc

@@ -66,6 +66,7 @@ class WidgetModalDialogHostObserverViews
       host_->RemoveObserver(this);
     target_widget_->RemoveObserver(this);
     target_widget_->SetNativeWindowProperty(native_window_property_, nullptr);
+    CHECK(!IsInObserverList());
   }
 
   // WidgetObserver overrides

components/constrained_window/native_web_contents_modal_dialog_manager_views.cc

@@ -50,6 +50,7 @@ NativeWebContentsModalDialogManagerViews::
 
   for (auto* widget : observed_widgets_)
     widget->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void NativeWebContentsModalDialogManagerViews::ManageDialog() {

components/exo/shell_surface_base.cc

@@ -337,6 +337,7 @@ ShellSurfaceBase::~ShellSurfaceBase() {
     root_surface()->RemoveSurfaceObserver(this);
   if (has_grab_)
     WMHelper::GetInstance()->GetCaptureClient()->RemoveObserver(this);
+  CHECK(!views::WidgetObserver::IsInObserverList());
 }
 
 void ShellSurfaceBase::Activate() {

components/ui_devtools/views/dom_agent_mac.mm

@@ -12,7 +12,10 @@
 namespace ui_devtools {
 
 DOMAgentMac::DOMAgentMac() {}
-DOMAgentMac::~DOMAgentMac() {}
+
+DOMAgentMac::~DOMAgentMac() {
+  CHECK(!IsInObserverList());
+}
 
 protocol::Response DOMAgentMac::enable() {
   views::NativeWidgetMac::SetInitNativeWidgetCallback(base::BindRepeating(

components/ui_devtools/views/overlay_agent_mac.mm

@@ -17,6 +17,7 @@ OverlayAgentMac::OverlayAgentMac(DOMAgent* dom_agent)
 OverlayAgentMac::~OverlayAgentMac() {
   if (is_pretarget_handler_)
     RemovePreTargetHandler();
+  CHECK(!IsInObserverList());
 }
 
 void OverlayAgentMac::InstallPreTargetHandler() {

components/ui_devtools/views/widget_element.cc

@@ -23,6 +23,7 @@ WidgetElement::~WidgetElement() {
     widget_->RemoveRemovalsObserver(this);
     widget_->RemoveObserver(this);
   }
+  CHECK(!IsInObserverList());
 }
 
 void WidgetElement::OnWillRemoveView(views::Widget* widget, views::View* view) {

extensions/components/native_app_window/native_app_window_views.cc

@@ -50,6 +50,7 @@ void NativeAppWindowViews::Init(
 
 NativeAppWindowViews::~NativeAppWindowViews() {
   web_view_->SetWebContents(nullptr);
+  CHECK(!IsInObserverList());
 }
 
 void NativeAppWindowViews::OnCanHaveAlphaEnabledChanged() {

ui/views/animation/compositor_animation_runner.cc

@@ -23,6 +23,7 @@ CompositorAnimationRunner::~CompositorAnimationRunner() {
   if (widget_)
     OnWidgetDestroying(widget_);
   DCHECK(!compositor_ || !compositor_->HasAnimationObserver(this));
+  CHECK(!IsInObserverList());
 }
 
 void CompositorAnimationRunner::SetAnimationMetricsReporter(

ui/views/controls/button/button.cc

@@ -56,6 +56,7 @@ Button::WidgetObserverButtonBridge::WidgetObserverButtonBridge(Button* button)
 Button::WidgetObserverButtonBridge::~WidgetObserverButtonBridge() {
   if (owner_)
     owner_->GetWidget()->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void Button::WidgetObserverButtonBridge::OnWidgetPaintAsActiveChanged(

ui/views/controls/menu/menu_controller.cc

@@ -1635,6 +1635,7 @@ MenuController::~MenuController() {
     active_instance_ = nullptr;
   StopShowTimer();
   StopCancelAllTimer();
+  CHECK(!IsInObserverList());
 }
 
 bool MenuController::SendAcceleratorToHotTrackedView() {

ui/views/controls/menu/menu_host.cc

@@ -103,6 +103,7 @@ MenuHost::MenuHost(SubmenuView* submenu)
 MenuHost::~MenuHost() {
   if (owner_)
     owner_->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void MenuHost::InitMenuHost(Widget* parent,

ui/views/corewm/tooltip_aura.cc

@@ -158,6 +158,7 @@ namespace corewm {
 
 TooltipAura::~TooltipAura() {
   DestroyWidget();
+  CHECK(!IsInObserverList());
 }
 
 class TooltipAura::TooltipWidget : public Widget {

ui/views/test/test_widget_observer.cc

@@ -17,6 +17,7 @@ TestWidgetObserver::TestWidgetObserver(Widget* widget) : widget_(widget) {
 TestWidgetObserver::~TestWidgetObserver() {
   if (widget_)
     widget_->RemoveObserver(this);
+  CHECK(!IsInObserverList());
 }
 
 void TestWidgetObserver::OnWidgetDestroying(Widget* widget) {

ui/views/touchui/touch_selection_controller_impl.cc

@@ -402,6 +402,7 @@ TouchSelectionControllerImpl::~TouchSelectionControllerImpl() {
   selection_handle_1_->CloseHandleWidget();
   selection_handle_2_->CloseHandleWidget();
   cursor_handle_->CloseHandleWidget();
+  CHECK(!IsInObserverList());
 }
 
 void TouchSelectionControllerImpl::SelectionChanged() {

ui/views/widget/widget_deletion_observer.cc

@@ -16,6 +16,7 @@ WidgetDeletionObserver::WidgetDeletionObserver(Widget* widget)
 
 WidgetDeletionObserver::~WidgetDeletionObserver() {
   CleanupWidget();
+  CHECK(!IsInObserverList());
 }
 
 void WidgetDeletionObserver::OnWidgetDestroying(Widget* widget) {