screenshot-window-sizer: Delay size popup

We use the actual frame size for the popup rather than the target
size. That means (on wayland), we have to wait for the size to
actually change.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/232>

extensions/screenshot-window-sizer/extension.js

@@ -121,8 +121,18 @@ function cycleScreenshotSizes(display, window, binding) {
     if (newY + newHeight > workArea.y + workArea.height)
         newY = Math.max(workArea.y + workArea.height - newHeight);
 
+    const id = window.connect('size-changed', () => {
+        window.disconnect(id);
+        _notifySizeChange(window);
+    });
     window.move_resize_frame(true, newX, newY, newWidth, newHeight);
+}
 
+/**
+ * @param {Meta.Window} window - the window whose size changed
+ */
+function _notifySizeChange(window) {
+    const { scaleFactor } = St.ThemeContext.get_for_stage(global.stage);
     let newOuterRect = window.get_frame_rect();
     let message = '%d×%d'.format(
         newOuterRect.width / scaleFactor,