appDisplay: Allow passing callback to AppFolderDialog.popdown()

Next commit will allow removing icons from the folder, and we want to
do that effectively after the dialog pops down.

Add an optional callback to AppFolderDialog.popdown().

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1447

js/ui/appDisplay.js

@@ -2093,6 +2093,8 @@ var AppFolderDialog = GObject.registerClass({
         this._sourceMappedId = 0;
         this._popdownTimeoutId = 0;
         this._needsZoomAndFade = false;
+
+        this._popdownCallbacks = [];
     }
 
     _addFolderNameEntry() {
@@ -2297,6 +2299,9 @@ var AppFolderDialog = GObject.registerClass({
                     opacity: 255,
                 });
                 this.hide();
+
+                this._popdownCallbacks.forEach(func => func());
+                this._popdownCallbacks = [];
             },
         });
 
@@ -2477,7 +2482,16 @@ var AppFolderDialog = GObject.registerClass({
         this.emit('open-state-changed', true);
     }
 
-    popdown() {
+    popdown(callback) {
+        // Either call the callback right away, or wait for the zoom out
+        // animation to finish
+        if (callback) {
+            if (this.visible)
+                this._popdownCallbacks.push(callback);
+            else
+                callback();
+        }
+
         if (!this._isOpen)
             return;