system: Track buttonGroup visibility using a group of actors

Cleanup the visibility check on actions by using an array of actors to
track, so that we don't repeat the same variables multiple times.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/700

js/ui/status/system.js

@@ -137,15 +137,6 @@ var Indicator = class extends PanelMenu.SystemIndicator {
         this._sessionUpdated();
     }
 
-    _updateActionsVisibility() {
-        let visible = (this._settingsAction.visible ||
-                       this._orientationLockAction.visible ||
-                       this._lockScreenAction.visible ||
-                       this._altSwitcher.actor.visible);
-
-        this.buttonGroup.visible = visible;
-    }
-
     _sessionUpdated() {
         this._settingsAction.visible = Main.sessionMode.allowSettings;
     }
@@ -302,15 +293,18 @@ var Indicator = class extends PanelMenu.SystemIndicator {
 
         this.menu.addMenuItem(item);
 
+        let visibilityGroup = [
+            this._settingsAction,
+            this._orientationLockAction,
+            this._lockScreenAction,
+            this._altSwitcher.actor,
+        ];
 
-        this._settingsAction.connect('notify::visible',
+        for (let actor of visibilityGroup) {
-                                     () => this._updateActionsVisibility());
+            actor.connect('notify::visible', () => {
-        this._orientationLockAction.connect('notify::visible',
+                this.buttonGroup.visible = visibilityGroup.some(a => a.visible);
-                                            () => this._updateActionsVisibility());
+            });
-        this._lockScreenAction.connect('notify::visible',
+        }
-                                       () => this._updateActionsVisibility());
-        this._altSwitcher.actor.connect('notify::visible',
-                                        () => this._updateActionsVisibility());
     }
 
     _onSettingsClicked() {