Introduce an ObserverList<T>::Unchecked type alias.

This is a precursor to https://crrev.com/c/1053338 which introduces
base::CheckedObserver. Existing observers will be unchecked (as they
are already). There is no behavior change with this CL.

The CL is mechanical. The bulk was done with variations on a sed script:

git grep -l ' base::ObserverList<.*> .*;' -- '*.cc' '*.h' '*.mm' | \
  xargs -IX sed -i -r 's/(^[ ]*)base::ObserverList<([^>]*)> (.*);/'\
    '\1base::ObserverList<\2>::Unchecked \3;/' X

With some manual follow-ups to get special cases.

TBR=gab@chromium.org

Bug: 842987
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:ios-simulator-full-configs;luci.chromium.try:linux_layout_tests_slimming_paint_v2;luci.chromium.try:linux_mojo;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Idffe88e2b52f67f9226eb7b6d922070349dacc22
Reviewed-on: https://chromium-review.googlesource.com/1175511
Commit-Queue: Trent Apted <tapted@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584330}

android_webview/browser/aw_render_thread_context_provider.h

@@ -74,7 +74,7 @@ class AwRenderThreadContextProvider
   sk_sp<class GrContext> gr_context_;
   std::unique_ptr<viz::ContextCacheController> cache_controller_;
 
-  base::ObserverList<viz::ContextLostObserver> observers_;
+  base::ObserverList<viz::ContextLostObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AwRenderThreadContextProvider);
 };

apps/app_lifetime_monitor.h

@@ -77,7 +77,7 @@ class AppLifetimeMonitor : public KeyedService,
 
   content::NotificationRegistrar registrar_;
   content::BrowserContext* context_;
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AppLifetimeMonitor);
 };

ash/accessibility/accessibility_controller.h

@@ -240,7 +240,7 @@ class ASH_EXPORT AccessibilityController
   // Used to force the backlights off to darken the screen.
   std::unique_ptr<ScopedBacklightsForcedOff> scoped_backlights_forced_off_;
 
-  base::ObserverList<AccessibilityObserver> observers_;
+  base::ObserverList<AccessibilityObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AccessibilityController);
 };

ash/app_list/model/app_list_item.h

@@ -139,7 +139,7 @@ class APP_LIST_MODEL_EXPORT AppListItem {
   bool is_installing_;
   int percent_downloaded_;
 
-  base::ObserverList<AppListItemObserver> observers_;
+  base::ObserverList<AppListItemObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListItem);
 };

ash/app_list/model/app_list_item_list.h

@@ -115,7 +115,7 @@ class APP_LIST_MODEL_EXPORT AppListItemList {
   void FixItemPosition(size_t index);
 
   std::vector<std::unique_ptr<AppListItem>> app_list_items_;
-  base::ObserverList<AppListItemListObserver, true> observers_;
+  base::ObserverList<AppListItemListObserver, true>::Unchecked observers_;
   std::string highlighted_id_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListItemList);

ash/app_list/model/app_list_model.h

@@ -164,7 +164,7 @@ class APP_LIST_MODEL_EXPORT AppListModel : public AppListItemListObserver {
   ash::AppListState state_ = ash::AppListState::kInvalidState;
   // The AppListView state. Controlled by the AppListView.
   AppListViewState state_fullscreen_ = AppListViewState::CLOSED;
-  base::ObserverList<AppListModelObserver, true> observers_;
+  base::ObserverList<AppListModelObserver, true>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListModel);
 };

ash/app_list/model/folder_image.h

@@ -107,7 +107,7 @@ class APP_LIST_MODEL_EXPORT FolderImage : public AppListItemListObserver,
   // True if new style launcher feature is enabled.
   const bool is_new_style_launcher_enabled_;
 
-  base::ObserverList<FolderImageObserver> observers_;
+  base::ObserverList<FolderImageObserver>::Unchecked observers_;
 };
 
 }  // namespace app_list

ash/app_list/model/search/search_box_model.h

@@ -78,7 +78,7 @@ class APP_LIST_MODEL_EXPORT SearchBoxModel {
   bool is_tablet_mode_ = false;
   bool show_assistant_button_ = false;
 
-  base::ObserverList<SearchBoxModelObserver> observers_;
+  base::ObserverList<SearchBoxModelObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SearchBoxModel);
 };

ash/app_list/model/search/search_result.h

@@ -150,7 +150,7 @@ class APP_LIST_MODEL_EXPORT SearchResult {
 
   ash::mojom::SearchResultMetadataPtr metadata_;
 
-  base::ObserverList<SearchResultObserver> observers_;
+  base::ObserverList<SearchResultObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SearchResult);
 };

ash/app_list/pagination_model.h

@@ -144,7 +144,7 @@ class APP_LIST_EXPORT PaginationModel : public gfx::AnimationDelegate {
 
   base::TimeTicks last_overscroll_animation_start_time_;
 
-  base::ObserverList<PaginationModelObserver> observers_;
+  base::ObserverList<PaginationModelObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(PaginationModel);
 };

ash/app_list/views/top_icon_animation_view.h

@@ -78,7 +78,7 @@ class TopIconAnimationView : public views::View,
 
   bool item_in_folder_icon_;
 
-  base::ObserverList<TopIconAnimationObserver> observers_;
+  base::ObserverList<TopIconAnimationObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(TopIconAnimationView);
 };

ash/assistant/assistant_controller.h

@@ -170,7 +170,7 @@ class ASH_EXPORT AssistantController
 
   // The observer list should be initialized early so that sub-controllers may
   // register as observers during their construction.
-  base::ObserverList<AssistantControllerObserver> observers_;
+  base::ObserverList<AssistantControllerObserver>::Unchecked observers_;
 
   mojo::BindingSet<mojom::AssistantController> assistant_controller_bindings_;
 

ash/assistant/model/assistant_interaction_model.h

@@ -139,7 +139,7 @@ class AssistantInteractionModel {
   std::unique_ptr<AssistantResponse> pending_response_;
   std::unique_ptr<AssistantResponse> response_;
 
-  base::ObserverList<AssistantInteractionModelObserver> observers_;
+  base::ObserverList<AssistantInteractionModelObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AssistantInteractionModel);
 };

ash/assistant/model/assistant_screen_context_model.h

@@ -35,7 +35,7 @@ class AssistantScreenContextModel {
 
   ScreenContextRequestState request_state_ = ScreenContextRequestState::kIdle;
 
-  base::ObserverList<AssistantScreenContextModelObserver> observers_;
+  base::ObserverList<AssistantScreenContextModelObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AssistantScreenContextModel);
 };

ash/assistant/model/assistant_ui_model.h

@@ -60,7 +60,7 @@ class AssistantUiModel {
 
   bool visible_ = false;
 
-  base::ObserverList<AssistantUiModelObserver> observers_;
+  base::ObserverList<AssistantUiModelObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AssistantUiModel);
 };

ash/assistant/ui/dialog_plate/dialog_plate.h

@@ -110,7 +110,7 @@ class DialogPlate : public views::View,
 
   std::unique_ptr<ui::CallbackLayerAnimationObserver> animation_observer_;
 
-  base::ObserverList<DialogPlateObserver> observers_;
+  base::ObserverList<DialogPlateObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(DialogPlate);
 };

ash/cast_config_controller.h

@@ -73,7 +73,7 @@ class CastConfigController : public ash::mojom::CastConfig {
 
   std::vector<mojom::SinkAndRoutePtr> sinks_and_routes_;
 
-  base::ObserverList<CastConfigControllerObserver> observers_;
+  base::ObserverList<CastConfigControllerObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(CastConfigController);
 };

ash/detachable_base/detachable_base_handler.h

@@ -155,7 +155,7 @@ class ASH_EXPORT DetachableBaseHandler
   // Used for ephemeral users.
   std::map<AccountId, DetachableBaseId> last_used_devices_;
 
-  base::ObserverList<DetachableBaseObserver> observers_;
+  base::ObserverList<DetachableBaseObserver>::Unchecked observers_;
 
   base::WeakPtrFactory<DetachableBaseHandler> weak_ptr_factory_;
 

ash/display/screen_orientation_controller.h

@@ -241,7 +241,7 @@ class ASH_EXPORT ScreenOrientationController
   display::Display::Rotation current_rotation_;
 
   // Rotation Lock observers.
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   // Tracks all windows that have requested a lock, as well as the requested
   // orientation.

ash/display/window_tree_host_manager.h

@@ -199,7 +199,7 @@ class ASH_EXPORT WindowTreeHostManager
   // The mapping from display ID to its window tree host.
   WindowTreeHostMap window_tree_hosts_;
 
-  base::ObserverList<Observer, true> observers_;
+  base::ObserverList<Observer, true>::Unchecked observers_;
 
   // Store the primary window tree host temporarily while replacing
   // display.

ash/drag_drop/drag_drop_controller.h

@@ -138,7 +138,8 @@ class ASH_EXPORT DragDropController : public aura::client::DragDropClient,
   // See comment in OnGestureEvent() on why we need this.
   std::unique_ptr<ui::GestureEvent> pending_long_tap_;
 
-  base::ObserverList<aura::client::DragDropClientObserver> observers_;
+  base::ObserverList<aura::client::DragDropClientObserver>::Unchecked
+      observers_;
 
   base::WeakPtrFactory<DragDropController> weak_factory_;
 

ash/highlighter/highlighter_controller.h

@@ -157,7 +157,7 @@ class ASH_EXPORT HighlighterController
   // Interface to highlighter controller client (chrome).
   mojom::HighlighterControllerClientPtr client_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   base::WeakPtrFactory<HighlighterController> weak_factory_;
 

ash/ime/ime_controller.h

@@ -167,7 +167,7 @@ class ASH_EXPORT ImeController : public mojom::ImeController {
   // True if voice input should be available from the IME menu.
   bool is_voice_enabled_ = false;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   std::unique_ptr<ModeIndicatorObserver> mode_indicator_observer_;
 

ash/keyboard/keyboard_ui.h

@@ -42,10 +42,12 @@ class ASH_EXPORT KeyboardUI {
  protected:
   KeyboardUI();
 
-  base::ObserverList<KeyboardUIObserver>* observers() { return &observers_; }
+  base::ObserverList<KeyboardUIObserver>::Unchecked* observers() {
+    return &observers_;
+  }
 
  private:
-  base::ObserverList<KeyboardUIObserver> observers_;
+  base::ObserverList<KeyboardUIObserver>::Unchecked observers_;
 };
 
 }  // namespace ash

ash/lock_screen_action/lock_screen_action_background_controller.h

@@ -85,7 +85,7 @@ class ASH_EXPORT LockScreenActionBackgroundController {
   LockScreenActionBackgroundState state_ =
       LockScreenActionBackgroundState::kHidden;
 
-  base::ObserverList<LockScreenActionBackgroundObserver> observers_;
+  base::ObserverList<LockScreenActionBackgroundObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(LockScreenActionBackgroundController);
 };

ash/login/login_screen_controller.h

@@ -177,7 +177,7 @@ class ASH_EXPORT LoginScreenController : public mojom::LoginScreen {
 
   AuthenticationStage authentication_stage_ = AuthenticationStage::kIdle;
 
-  base::ObserverList<LoginScreenControllerObserver> observers_;
+  base::ObserverList<LoginScreenControllerObserver>::Unchecked observers_;
 
   // If set to false, all auth requests will forcibly fail.
   ForceFailAuth force_fail_auth_for_debug_overlay_ = ForceFailAuth::kOff;

ash/login/ui/login_data_dispatcher.h

@@ -153,7 +153,7 @@ class ASH_EXPORT LoginDataDispatcher {
                                  mojom::FingerprintUnlockState state);
 
  private:
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(LoginDataDispatcher);
 };

ash/media_controller.h

@@ -57,7 +57,7 @@ class MediaController : public mojom::MediaController {
 
   mojom::MediaClientAssociatedPtr client_;
 
-  base::ObserverList<MediaCaptureObserver> observers_;
+  base::ObserverList<MediaCaptureObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaController);
 };

ash/message_center/message_center_controller.h

@@ -103,7 +103,8 @@ class ASH_EXPORT MessageCenterController
       session_state_notification_blocker_;
   std::unique_ptr<message_center::NotificationBlocker> all_popup_blocker_;
 
-  base::ObserverList<NotifierSettingsListener> notifier_settings_listeners_;
+  base::ObserverList<NotifierSettingsListener>::Unchecked
+      notifier_settings_listeners_;
 
   mojo::BindingSet<mojom::AshMessageCenterController> binding_set_;
 

ash/message_center/message_list_view.h

@@ -134,7 +134,7 @@ class ASH_EXPORT MessageListView : public views::View,
   void AnimateClearingOneNotification();
 
   // List of MessageListView::Observer
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   // The top position of the reposition target rectangle.
   int reposition_top_;

ash/pointer_watcher_adapter.h

@@ -58,9 +58,9 @@ class ASH_EXPORT PointerWatcherAdapter : public ui::EventHandler {
   // destruction. Two sets of observers are maintained, one for observers not
   // needing moves |non_move_watchers_| and |move_watchers_| for those
   // observers wanting moves too.
-  base::ObserverList<views::PointerWatcher, true> non_move_watchers_;
+  base::ObserverList<views::PointerWatcher, true>::Unchecked non_move_watchers_;
-  base::ObserverList<views::PointerWatcher, true> move_watchers_;
+  base::ObserverList<views::PointerWatcher, true>::Unchecked move_watchers_;
-  base::ObserverList<views::PointerWatcher, true> drag_watchers_;
+  base::ObserverList<views::PointerWatcher, true>::Unchecked drag_watchers_;
 
   DISALLOW_COPY_AND_ASSIGN(PointerWatcherAdapter);
 };

ash/public/cpp/shelf_model.h

@@ -128,7 +128,7 @@ class ASH_PUBLIC_EXPORT ShelfModel {
   // Maps one notification id to one app id.
   std::map<std::string, std::string> notification_id_to_app_id_;
 
-  base::ObserverList<ShelfModelObserver> observers_;
+  base::ObserverList<ShelfModelObserver>::Unchecked observers_;
 
   std::map<ShelfID, std::unique_ptr<ShelfItemDelegate>>
       id_to_item_delegate_map_;

ash/rotator/screen_rotation_animator.h

@@ -180,7 +180,7 @@ class ASH_EXPORT ScreenRotationAnimator {
   std::unique_ptr<ui::AnimationMetricsReporter> metrics_reporter_;
   // Only set in unittest to disable animation timers.
   bool disable_animation_timers_for_test_;
-  base::ObserverList<ScreenRotationAnimatorObserver>
+  base::ObserverList<ScreenRotationAnimatorObserver>::Unchecked
       screen_rotation_animator_observers_;
   std::unique_ptr<ui::LayerTreeOwner> old_layer_tree_owner_;
   std::unique_ptr<ui::LayerTreeOwner> new_layer_tree_owner_;

ash/session/session_controller.h

@@ -288,7 +288,7 @@ class ASH_EXPORT SessionController : public mojom::SessionController {
   // OnSigninScreenPrefServiceInitialized().
   bool on_active_user_prefs_changed_notify_deferred_ = false;
 
-  base::ObserverList<ash::SessionObserver> observers_;
+  base::ObserverList<ash::SessionObserver>::Unchecked observers_;
 
   service_manager::Connector* const connector_;
 

ash/shelf/shelf.h

@@ -178,7 +178,7 @@ class ASH_EXPORT Shelf : public ShelfLayoutManagerObserver {
   // Sets shelf alignment to bottom during login and screen lock.
   ShelfLockingManager shelf_locking_manager_;
 
-  base::ObserverList<ShelfObserver> observers_;
+  base::ObserverList<ShelfObserver>::Unchecked observers_;
 
   // Forwards mouse and gesture events to ShelfLayoutManager for auto-hide.
   std::unique_ptr<AutoHideEventHandler> auto_hide_event_handler_;

ash/shelf/shelf_background_animator.h

@@ -178,7 +178,7 @@ class ASH_EXPORT ShelfBackgroundAnimator : public ShelfObserver,
   // Tracks the item background animation values.
   AnimationValues item_background_values_;
 
-  base::ObserverList<ShelfBackgroundAnimatorObserver> observers_;
+  base::ObserverList<ShelfBackgroundAnimatorObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfBackgroundAnimator);
 };

ash/shelf/shelf_button.cc

@@ -125,7 +125,7 @@ class ShelfButtonAnimation : public gfx::AnimationDelegate {
   }
 
   gfx::ThrobAnimation animation_;
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfButtonAnimation);
 };

ash/shelf/shelf_layout_manager.h

@@ -362,7 +362,7 @@ class ASH_EXPORT ShelfLayoutManager
   // False when neither the auto hide timer nor the timer task are running.
   bool mouse_over_shelf_when_auto_hide_timer_started_ = false;
 
-  base::ObserverList<ShelfLayoutManagerObserver> observers_;
+  base::ObserverList<ShelfLayoutManagerObserver>::Unchecked observers_;
 
   // The shelf reacts to gesture-drags, and can be set to auto-hide for certain
   // gestures. Swiping up from the shelf in tablet mode can open the

ash/shell.h

@@ -900,7 +900,7 @@ class ASH_EXPORT Shell : public SessionObserver,
 
   std::unique_ptr<MessageCenterController> message_center_controller_;
 
-  base::ObserverList<ShellObserver> shell_observers_;
+  base::ObserverList<ShellObserver>::Unchecked shell_observers_;
 
   base::WeakPtrFactory<Shell> weak_factory_;
 

ash/shutdown_controller.h

@@ -54,7 +54,7 @@ class ASH_EXPORT ShutdownController : public mojom::ShutdownController {
   // Cached copy of the DeviceRebootOnShutdown policy from chrome.
   bool reboot_on_shutdown_ = false;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   // Bindings for the ShutdownController interface.
   mojo::BindingSet<mojom::ShutdownController> bindings_;

ash/system/message_center/arc/arc_notification_item_impl.h

@@ -73,7 +73,7 @@ class ArcNotificationItemImpl : public ArcNotificationItem {
   // The reference counter of the window.
   int window_ref_count_ = 0;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   const AccountId profile_id_;
   const std::string notification_key_;

ash/system/message_center/arc/arc_notification_surface_manager_impl.h

@@ -43,7 +43,7 @@ class ArcNotificationSurfaceManagerImpl
                          std::unique_ptr<ArcNotificationSurfaceImpl>>;
   NotificationSurfaceMap notification_surface_map_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcNotificationSurfaceManagerImpl);
 };

ash/system/message_center/arc/mock_arc_notification_item.h

@@ -60,7 +60,7 @@ class MockArcNotificationItem : public ArcNotificationItem {
   gfx::ImageSkia snapshot_;
   size_t count_close_ = 0;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
   base::OnceClosure close_callback_;
 
   base::WeakPtrFactory<MockArcNotificationItem> weak_factory_;

ash/system/model/clock_model.h

@@ -62,7 +62,7 @@ class ClockModel : public chromeos::SystemClockClient::Observer,
   // If system clock can be configured by user through SetTimeDialog.
   bool can_set_time_ = false;
 
-  base::ObserverList<ClockObserver> observers_;
+  base::ObserverList<ClockObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ClockModel);
 };

ash/system/model/enterprise_domain_model.h

@@ -42,7 +42,7 @@ class ASH_EXPORT EnterpriseDomainModel {
   // Whether this is an Active Directory managed enterprise device.
   bool active_directory_managed_ = false;
 
-  base::ObserverList<EnterpriseDomainObserver> observers_;
+  base::ObserverList<EnterpriseDomainObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(EnterpriseDomainModel);
 };

ash/system/model/session_length_limit_model.h

@@ -52,7 +52,7 @@ class SessionLengthLimitModel : public SessionObserver {
 
   std::unique_ptr<base::RepeatingTimer> timer_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionLengthLimitModel);
 };

ash/system/model/tracing_model.h

@@ -40,7 +40,7 @@ class ASH_EXPORT TracingModel {
   // True if performance tracing is enabled.
   bool is_tracing_ = false;
 
-  base::ObserverList<TracingObserver> observers_;
+  base::ObserverList<TracingObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(TracingModel);
 };

ash/system/model/update_model.h

@@ -62,7 +62,7 @@ class UpdateModel {
   mojom::UpdateType update_type_ = mojom::UpdateType::SYSTEM;
   bool update_over_cellular_available_ = false;
 
-  base::ObserverList<UpdateObserver> observers_;
+  base::ObserverList<UpdateObserver>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(UpdateModel);
 };

ash/system/network/network_icon_animation.h

@@ -39,7 +39,7 @@ class ASH_EXPORT NetworkIconAnimation : public gfx::AnimationDelegate {
 
  private:
   gfx::ThrobAnimation animation_;
-  base::ObserverList<AnimationObserver> observers_;
+  base::ObserverList<AnimationObserver>::Unchecked observers_;
 };
 
 }  // namespace network_icon

ash/system/network/vpn_list.h

@@ -132,7 +132,7 @@ class ASH_EXPORT VpnList : public mojom::VpnList {
   // creating vpn list view.
   std::vector<VPNProvider> arc_vpn_providers_;
 
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(VpnList);
 };

ash/system/night_light/night_light_controller.h

@@ -230,7 +230,7 @@ class ASH_EXPORT NightLightController
   // controlled by this class from the WebUI settings.
   std::unique_ptr<PrefChangeRegistrar> pref_change_registrar_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   mojo::Binding<mojom::NightLightController> binding_;
 

ash/system/power/backlights_forced_off_setter.h

@@ -112,7 +112,7 @@ class ASH_EXPORT BacklightsForcedOffSetter
   // Number of active backlights forced off requests.
   int active_backlights_forced_off_count_ = 0;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   ScopedObserver<chromeos::PowerManagerClient,
                  chromeos::PowerManagerClient::Observer>

ash/system/power/power_status.h

@@ -208,7 +208,7 @@ class ASH_EXPORT PowerStatus : public chromeos::PowerManagerClient::Observer {
   // Overriden from PowerManagerClient::Observer.
   void PowerChanged(const power_manager::PowerSupplyProperties& proto) override;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   // Current state.
   power_manager::PowerSupplyProperties proto_;

ash/system/tray/system_tray_notifier.h

@@ -76,13 +76,16 @@ class ASH_EXPORT SystemTrayNotifier {
   void NotifyVirtualKeyboardSuppressionChanged(bool suppressed);
 
  private:
-  base::ObserverList<BluetoothObserver> bluetooth_observers_;
+  base::ObserverList<BluetoothObserver>::Unchecked bluetooth_observers_;
-  base::ObserverList<IMEObserver> ime_observers_;
+  base::ObserverList<IMEObserver>::Unchecked ime_observers_;
-  base::ObserverList<NetworkObserver> network_observers_;
+  base::ObserverList<NetworkObserver>::Unchecked network_observers_;
-  base::ObserverList<ScreenCaptureObserver> screen_capture_observers_;
+  base::ObserverList<ScreenCaptureObserver>::Unchecked
-  base::ObserverList<ScreenShareObserver> screen_share_observers_;
+      screen_capture_observers_;
-  base::ObserverList<SystemTrayFocusObserver> system_tray_focus_observers_;
+  base::ObserverList<ScreenShareObserver>::Unchecked screen_share_observers_;
-  base::ObserverList<VirtualKeyboardObserver> virtual_keyboard_observers_;
+  base::ObserverList<SystemTrayFocusObserver>::Unchecked
+      system_tray_focus_observers_;
+  base::ObserverList<VirtualKeyboardObserver>::Unchecked
+      virtual_keyboard_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayNotifier);
 };

ash/system/unified/unified_system_tray_model.h

@@ -58,7 +58,7 @@ class ASH_EXPORT UnifiedSystemTrayModel {
 
   std::unique_ptr<DBusObserver> dbus_observer_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(UnifiedSystemTrayModel);
 };

ash/tray_action/tray_action.h

@@ -90,7 +90,7 @@ class ASH_EXPORT TrayAction : public mojom::TrayAction,
   std::unique_ptr<LockScreenNoteDisplayStateHandler>
       lock_screen_note_display_state_handler_;
 
-  base::ObserverList<TrayActionObserver> observers_;
+  base::ObserverList<TrayActionObserver>::Unchecked observers_;
 
   // Bindings for users of the mojo interface.
   mojo::BindingSet<mojom::TrayAction> bindings_;

ash/wallpaper/wallpaper_controller.h

@@ -542,7 +542,7 @@ class ASH_EXPORT WallpaperController : public mojom::WallpaperController,
   // Bindings for the WallpaperController interface.
   mojo::BindingSet<mojom::WallpaperController> bindings_;
 
-  base::ObserverList<WallpaperControllerObserver> observers_;
+  base::ObserverList<WallpaperControllerObserver>::Unchecked observers_;
 
   mojo::AssociatedInterfacePtrSet<mojom::WallpaperObserver> mojo_observers_;
 

ash/wallpaper/wallpaper_utils/wallpaper_color_calculator.h

@@ -78,7 +78,7 @@ class ASH_EXPORT WallpaperColorCalculator {
   // The task runner to run the calculation on.
   scoped_refptr<base::TaskRunner> task_runner_;
 
-  base::ObserverList<WallpaperColorCalculatorObserver> observers_;
+  base::ObserverList<WallpaperColorCalculatorObserver>::Unchecked observers_;
 
   base::WeakPtrFactory<WallpaperColorCalculator> weak_ptr_factory_;
 

ash/wallpaper/wallpaper_utils/wallpaper_resizer.h

@@ -61,7 +61,7 @@ class ASH_EXPORT WallpaperResizer {
   // has finished running.
   void OnResizeFinished(SkBitmap* resized_bitmap);
 
-  base::ObserverList<WallpaperResizerObserver> observers_;
+  base::ObserverList<WallpaperResizerObserver>::Unchecked observers_;
 
   // Image that should currently be used for wallpaper. It initially
   // contains the original image and is updated to contain the resized

ash/wm/lock_state_controller.h

@@ -251,7 +251,7 @@ class ASH_EXPORT LockStateController : public aura::WindowTreeHostObserver,
 
   ScopedSessionObserver scoped_session_observer_;
 
-  base::ObserverList<LockStateObserver> observers_;
+  base::ObserverList<LockStateObserver>::Unchecked observers_;
 
   base::WeakPtrFactory<LockStateController> weak_ptr_factory_;
 

ash/wm/splitview/split_view_controller.h

@@ -398,7 +398,7 @@ class ASH_EXPORT SplitViewController : public mojom::SplitViewController,
   // window comes from the overview.
   base::flat_map<aura::Window*, gfx::Rect> overview_window_item_bounds_map_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
   mojo::InterfacePtrSet<mojom::SplitViewObserver> mojo_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(SplitViewController);

ash/wm/tablet_mode/tablet_mode_controller.h

@@ -279,7 +279,7 @@ class ASH_EXPORT TabletModeController
 
   ScopedSessionObserver scoped_session_observer_;
 
-  base::ObserverList<TabletModeObserver> tablet_mode_observers_;
+  base::ObserverList<TabletModeObserver>::Unchecked tablet_mode_observers_;
 
   base::WeakPtrFactory<TabletModeController> weak_factory_;
 

ash/wm/video_detector.h

@@ -98,7 +98,7 @@ class ASH_EXPORT VideoDetector : public aura::EnvObserver,
   // Currently-fullscreen root windows.
   std::set<aura::Window*> fullscreen_root_windows_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   ScopedObserver<aura::Window, aura::WindowObserver> window_observer_manager_;
   ScopedSessionObserver scoped_session_observer_;

ash/wm/window_state.h

@@ -438,7 +438,7 @@ class ASH_EXPORT WindowState : public aura::WindowObserver {
   // displays are restored to their previous states.
   base::Optional<PersistentWindowInfo> persistent_window_info_;
 
-  base::ObserverList<WindowStateObserver> observer_list_;
+  base::ObserverList<WindowStateObserver>::Unchecked observer_list_;
 
   // True to ignore a property change event to avoid reentrance in
   // UpdateWindowStateType()

base/memory/memory_pressure_listener.cc

@@ -44,7 +44,7 @@ class MemoryPressureObserver {
   const scoped_refptr<ObserverListThreadSafe<MemoryPressureListener>>
       async_observers_ = base::MakeRefCounted<
           ObserverListThreadSafe<MemoryPressureListener>>();
-  ObserverList<MemoryPressureListener> sync_observers_;
+  ObserverList<MemoryPressureListener>::Unchecked sync_observers_;
   Lock sync_observers_lock_;
 };
 

base/message_loop/message_loop.h

@@ -287,7 +287,7 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate,
   // A recent snapshot of Time::Now(), used to check delayed_work_queue_.
   TimeTicks recent_time_;
 
-  ObserverList<DestructionObserver> destruction_observers_;
+  ObserverList<DestructionObserver>::Unchecked destruction_observers_;
 
   // A boolean which prevents unintentional reentrant task execution (e.g. from
   // induced nested message loops). As such, nested message loops will only
@@ -303,7 +303,7 @@ class BASE_EXPORT MessageLoop : public MessagePump::Delegate,
   // if type_ is TYPE_CUSTOM and pump_ is null.
   MessagePumpFactoryCallback pump_factory_;
 
-  ObserverList<TaskObserver> task_observers_;
+  ObserverList<TaskObserver>::Unchecked task_observers_;
 
   // Pointer to this MessageLoop's Controller, valid throughout this
   // MessageLoop's lifetime (until |underlying_task_runner_| is released at the

base/message_loop/message_pump_win.h

@@ -152,7 +152,7 @@ class BASE_EXPORT MessagePumpForUI : public MessagePumpWin {
   // TODO(thestig): Remove when the Cloud Print Service goes away.
   bool enable_wm_quit_ = false;
 
-  ObserverList<Observer> observers_;
+  ObserverList<Observer>::Unchecked observers_;
 };
 
 //-----------------------------------------------------------------------------

base/observer_list.h

@@ -99,6 +99,12 @@ class ObserverList
     : public SupportsWeakPtr<
           ObserverList<ObserverType, check_empty, allow_reentrancy>> {
  public:
+  // Temporary type alias for introducing base::CheckedObserver. Existing
+  // ObserverLists will be Unchecked during the migration.
+  // TODO(https://crbug.com/842987): Use the Unchecked storage type when that
+  // template param is added.
+  using Unchecked = ObserverList<ObserverType, check_empty, allow_reentrancy>;
+
   // An iterator class that can be used to access the list of observers.
   class Iter {
    public:

base/process/port_provider_mac.h

@@ -51,7 +51,7 @@ class BASE_EXPORT PortProvider {
   // ObserverList is not thread-safe, so |lock_| ensures consistency of
   // |observer_list_|.
   base::Lock lock_;
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(PortProvider);
 };

base/run_loop.h

@@ -194,7 +194,7 @@ class BASE_EXPORT RunLoop {
     using RunLoopStack = base::stack<RunLoop*, std::vector<RunLoop*>>;
 
     RunLoopStack active_run_loops_;
-    ObserverList<RunLoop::NestingObserver> nesting_observers_;
+    ObserverList<RunLoop::NestingObserver>::Unchecked nesting_observers_;
 
 #if DCHECK_IS_ON()
     bool allow_running_for_testing_ = true;

base/task/sequence_manager/sequence_manager_impl.h

@@ -222,8 +222,8 @@ class BASE_EXPORT SequenceManagerImpl
     std::uniform_real_distribution<double> uniform_distribution;
 
     internal::TaskQueueSelector selector;
-    ObserverList<MessageLoop::TaskObserver> task_observers;
+    ObserverList<MessageLoop::TaskObserver>::Unchecked task_observers;
-    ObserverList<TaskTimeObserver> task_time_observers;
+    ObserverList<TaskTimeObserver>::Unchecked task_time_observers;
     std::set<TimeDomain*> time_domains;
     std::unique_ptr<internal::RealTimeDomain> real_time_domain;
 

base/task/sequence_manager/task_queue_impl.h

@@ -355,7 +355,7 @@ class BASE_EXPORT TaskQueueImpl {
     std::unique_ptr<WorkQueue> delayed_work_queue;
     std::unique_ptr<WorkQueue> immediate_work_queue;
     std::priority_queue<TaskQueueImpl::Task> delayed_incoming_queue;
-    ObserverList<MessageLoop::TaskObserver> task_observers;
+    ObserverList<MessageLoop::TaskObserver>::Unchecked task_observers;
     size_t set_index;
     HeapHandle heap_handle;
     int is_enabled_refcount;

cc/animation/element_animations.h

@@ -64,7 +64,7 @@ class CC_ANIMATION_EXPORT ElementAnimations
   void RemoveKeyframeEffect(KeyframeEffect* keyframe_effect);
   bool IsEmpty() const;
 
-  typedef base::ObserverList<KeyframeEffect> KeyframeEffectsList;
+  typedef base::ObserverList<KeyframeEffect>::Unchecked KeyframeEffectsList;
   const KeyframeEffectsList& keyframe_effects_list() const {
     return keyframe_effects_list_;
   }

chrome/browser/android/bookmarks/partner_bookmarks_shim.h

@@ -140,7 +140,7 @@ class PartnerBookmarksShim : public base::SupportsUserData::Data {
   NodeRenamingMap node_rename_remove_map_;
 
   // The observers.
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(PartnerBookmarksShim);
 };

chrome/browser/android/thumbnail/thumbnail_cache.h

@@ -159,7 +159,7 @@ class ThumbnailCache : ThumbnailDelegate {
 
   ExpiringThumbnailCache cache_;
   ExpiringThumbnailCache approximation_cache_;
-  base::ObserverList<ThumbnailCacheObserver> observers_;
+  base::ObserverList<ThumbnailCacheObserver>::Unchecked observers_;
   ThumbnailMetaDataMap thumbnail_meta_data_;
   TabIdList read_queue_;
   TabIdList visible_ids_;

chrome/browser/background/background_application_list_model.h

@@ -159,7 +159,7 @@ class BackgroundApplicationListModel
   std::map<std::string, std::unique_ptr<Application>> applications_;
 
   extensions::ExtensionList extensions_;
-  base::ObserverList<Observer, true> observers_;
+  base::ObserverList<Observer, true>::Unchecked observers_;
   Profile* const profile_;
   content::NotificationRegistrar registrar_;
   bool ready_;

chrome/browser/background/background_contents.h

@@ -115,7 +115,7 @@ class BackgroundContents : public extensions::DeferredStartRenderHost,
   Profile* profile_;
   std::unique_ptr<content::WebContents> web_contents_;
   content::NotificationRegistrar registrar_;
-  base::ObserverList<extensions::DeferredStartRenderHostObserver>
+  base::ObserverList<extensions::DeferredStartRenderHostObserver>::Unchecked
       deferred_start_render_host_observer_list_;
 
   // The initial URL to load.

chrome/browser/browsing_data/cookies_tree_model.h

@@ -969,7 +969,7 @@ class CookiesTreeModel : public ui::TreeNodeModel<CookieTreeNode> {
 
   // The CookiesTreeModel maintains a separate list of observers that are
   // specifically of the type CookiesTreeModel::Observer.
-  base::ObserverList<Observer> cookies_observer_list_;
+  base::ObserverList<Observer>::Unchecked cookies_observer_list_;
 
   // Keeps track of how many batches the consumer of this class says it is going
   // to send.

chrome/browser/chrome_browser_application_mac.mm

@@ -101,7 +101,8 @@ std::string DescriptionForNSEvent(NSEvent* event) {
 @end
 
 @interface BrowserCrApplication ()<NativeEventProcessor> {
-  base::ObserverList<content::NativeEventProcessorObserver> observers_;
+  base::ObserverList<content::NativeEventProcessorObserver>::Unchecked
+      observers_;
 }
 @end
 

chrome/browser/chromeos/app_mode/arc/arc_kiosk_app_manager.h

@@ -87,7 +87,7 @@ class ArcKioskAppManager {
   std::vector<std::unique_ptr<ArcKioskAppData>> apps_;
   AccountId auto_launch_account_id_;
   bool auto_launched_with_zero_delay_ = false;
-  base::ObserverList<ArcKioskAppManagerObserver, true> observers_;
+  base::ObserverList<ArcKioskAppManagerObserver, true>::Unchecked observers_;
 
   std::unique_ptr<CrosSettings::ObserverSubscription>
       local_accounts_subscription_;

chrome/browser/chromeos/app_mode/kiosk_app_manager.h

@@ -361,7 +361,7 @@ class KioskAppManager : public KioskAppDataDelegate,
   std::vector<std::unique_ptr<KioskAppData>> apps_;
   std::string auto_launch_app_id_;
   std::string currently_auto_launched_with_zero_delay_app_;
-  base::ObserverList<KioskAppManagerObserver, true> observers_;
+  base::ObserverList<KioskAppManagerObserver, true>::Unchecked observers_;
 
   std::unique_ptr<CrosSettings::ObserverSubscription>
       local_accounts_subscription_;

chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge_unittest.cc

@@ -111,7 +111,7 @@ class ArcAccessibilityHelperBridgeTest : public ChromeViewsTestBase {
 
    private:
     std::map<std::string, ArcNotificationSurface*> surfaces_;
-    base::ObserverList<Observer> observers_;
+    base::ObserverList<Observer>::Unchecked observers_;
   };
 
   ArcAccessibilityHelperBridgeTest() = default;

chrome/browser/chromeos/arc/arc_session_manager.h

@@ -367,7 +367,7 @@ class ArcSessionManager : public ArcSessionRunner::Observer,
   // Internal state machine. See also State enum class.
   State state_ = State::NOT_INITIALIZED;
 
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
   std::unique_ptr<ArcAppLauncher> playstore_launcher_;
   bool reenable_arc_ = false;
   bool provisioning_reported_ = false;

chrome/browser/chromeos/arc/arc_session_manager_unittest.cc

@@ -1146,7 +1146,7 @@ class ArcSessionOobeOptInNegotiatorTest
 
   void Bind(chromeos::ArcTermsOfServiceScreen* screen) override {}
 
-  base::ObserverList<chromeos::ArcTermsOfServiceScreenViewObserver>
+  base::ObserverList<chromeos::ArcTermsOfServiceScreenViewObserver>::Unchecked
       observer_list_;
   std::unique_ptr<chromeos::FakeLoginDisplayHost> fake_login_display_host_;
 

chrome/browser/chromeos/arc/extensions/fake_arc_support.h

@@ -137,7 +137,7 @@ class FakeArcSupport : public extensions::NativeMessageHost::Client {
   bool tos_shown_ = false;
   std::string active_directory_auth_federation_url_;
   std::string active_directory_auth_device_management_url_prefix_;
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   base::WeakPtrFactory<FakeArcSupport> weak_ptr_factory_;
 

chrome/browser/chromeos/arc/fileapi/arc_file_system_bridge.h

@@ -105,7 +105,7 @@ class ArcFileSystemBridge : public KeyedService, public mojom::FileSystemHost {
 
   Profile* const profile_;
   ArcBridgeService* const bridge_service_;  // Owned by ArcServiceManager
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   // Map from file descriptor IDs to requested URLs.
   std::map<std::string, GURL> id_to_url_;

chrome/browser/chromeos/arc/fileapi/arc_file_system_operation_runner.h

@@ -191,7 +191,7 @@ class ArcFileSystemOperationRunner
   // Map from a watcher ID to a watcher callback.
   std::map<int64_t, WatcherCallback> watcher_callbacks_;
 
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   base::WeakPtrFactory<ArcFileSystemOperationRunner> weak_ptr_factory_;
 

chrome/browser/chromeos/arc/policy/arc_policy_bridge.h

@@ -176,7 +176,7 @@ class ArcPolicyBridge : public KeyedService,
   // since the most recent policy update notificaton was already reported.
   bool compliance_since_update_timing_reported_ = false;
 
-  base::ObserverList<Observer, true /* check_empty */> observers_;
+  base::ObserverList<Observer, true /* check_empty */>::Unchecked observers_;
 
   // Called when the ARC connection is ready.
   base::OnceClosure on_arc_instance_ready_callback_;

chrome/browser/chromeos/arc/voice_interaction/voice_interaction_controller_client.h

@@ -87,7 +87,7 @@ class VoiceInteractionControllerClient
   ash::mojom::VoiceInteractionState voice_interaction_state_ =
       ash::mojom::VoiceInteractionState::STOPPED;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   DISALLOW_COPY_AND_ASSIGN(VoiceInteractionControllerClient);
 };

chrome/browser/chromeos/camera_presence_notifier.h

@@ -43,7 +43,7 @@ class CameraPresenceNotifier {
   // Timer for camera check cycle.
   base::RepeatingTimer camera_check_timer_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   base::WeakPtrFactory<CameraPresenceNotifier> weak_factory_;
 

chrome/browser/chromeos/crostini/crostini_manager.cc

@@ -369,7 +369,8 @@ class CrostiniRestarter : public base::RefCountedThreadSafe<CrostiniRestarter>,
   std::string container_username_;
   std::string source_path_;
   CrostiniManager::RestartCrostiniCallback callback_;
-  base::ObserverList<CrostiniManager::RestartObserver> observer_list_;
+  base::ObserverList<CrostiniManager::RestartObserver>::Unchecked
+      observer_list_;
   CrostiniManager::RestartId restart_id_;
   CrostiniRestarterService* restarter_service_;
   bool is_aborted_ = false;

chrome/browser/chromeos/crostini/crostini_registry_service.h

@@ -205,7 +205,7 @@ class CrostiniRegistryService : public KeyedService {
   // stored.
   base::FilePath base_icon_path_;
 
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
 
   const base::Clock* clock_;
 

chrome/browser/chromeos/drive/drive_integration_service.h

@@ -227,7 +227,7 @@ class DriveIntegrationService : public KeyedService,
   std::unique_ptr<DownloadHandler> download_handler_;
   std::unique_ptr<DebugInfoCollector> debug_info_collector_;
 
-  base::ObserverList<DriveIntegrationServiceObserver> observers_;
+  base::ObserverList<DriveIntegrationServiceObserver>::Unchecked observers_;
   std::unique_ptr<PreferenceWatcher> preference_watcher_;
   std::unique_ptr<content::NotificationRegistrar>
       profile_notification_registrar_;

chrome/browser/chromeos/file_manager/fake_disk_mount_manager.h

@@ -106,7 +106,7 @@ class FakeDiskMountManager : public chromeos::disks::DiskMountManager {
                               const chromeos::disks::Disk* disk);
 
  private:
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
   base::queue<UnmountPathCallback> pending_unmount_callbacks_;
 
   DiskMap disks_;

chrome/browser/chromeos/file_manager/volume_manager.h

@@ -381,7 +381,7 @@ class VolumeManager : public KeyedService,
   drive::DriveIntegrationService* drive_integration_service_;  // Not owned.
   chromeos::disks::DiskMountManager* disk_mount_manager_;      // Not owned.
   PrefChangeRegistrar pref_change_registrar_;
-  base::ObserverList<VolumeManagerObserver> observers_;
+  base::ObserverList<VolumeManagerObserver>::Unchecked observers_;
   chromeos::file_system_provider::Service*
       file_system_provider_service_;  // Not owned by this class.
   GetMtpStorageInfoCallback get_mtp_storage_info_callback_;

chrome/browser/chromeos/file_system_provider/fake_provided_file_system.h

@@ -183,7 +183,7 @@ class FakeProvidedFileSystem : public ProvidedFileSystemInterface {
   OpenedFiles opened_files_;
   int last_file_handle_;
   base::CancelableTaskTracker tracker_;
-  base::ObserverList<ProvidedFileSystemObserver> observers_;
+  base::ObserverList<ProvidedFileSystemObserver>::Unchecked observers_;
   Watchers watchers_;
 
   base::WeakPtrFactory<FakeProvidedFileSystem> weak_ptr_factory_;

chrome/browser/chromeos/file_system_provider/provided_file_system.h

@@ -249,7 +249,7 @@ class ProvidedFileSystem : public ProvidedFileSystemInterface {
   Watchers watchers_;
   Queue watcher_queue_;
   OpenedFiles opened_files_;
-  base::ObserverList<ProvidedFileSystemObserver> observers_;
+  base::ObserverList<ProvidedFileSystemObserver>::Unchecked observers_;
 
   base::WeakPtrFactory<ProvidedFileSystem> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(ProvidedFileSystem);

chrome/browser/chromeos/file_system_provider/request_manager.h

@@ -185,7 +185,7 @@ class RequestManager {
   NotificationManagerInterface* notification_manager_;  // Not owned.
   int next_id_;
   base::TimeDelta timeout_;
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
   base::WeakPtrFactory<RequestManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RequestManager);

chrome/browser/chromeos/file_system_provider/service.h

@@ -203,7 +203,7 @@ class Service : public KeyedService,
 
   Profile* profile_;
   extensions::ExtensionRegistry* extension_registry_;  // Not owned.
-  base::ObserverList<Observer> observers_;
+  base::ObserverList<Observer>::Unchecked observers_;
   std::map<FileSystemKey, std::unique_ptr<ProvidedFileSystemInterface>>
       file_system_map_;
   std::map<std::string, FileSystemKey> mount_point_name_to_key_map_;

chrome/browser/chromeos/first_run/drive_first_run_controller.h

@@ -82,7 +82,7 @@ class DriveFirstRunController {
   base::OneShotTimer web_contents_timer_;
   base::OneShotTimer initial_delay_timer_;
   bool started_;
-  base::ObserverList<Observer> observer_list_;
+  base::ObserverList<Observer>::Unchecked observer_list_;
 
   int initial_delay_secs_;
   int web_contents_timeout_secs_;