Goldwave helped find more missing functionality.

list_view.h

@@ -8,8 +8,10 @@ struct ListViewRow {
   int index = -1;
   int count = 0;
   bool selected = false;
+  int checked = -1; // -1: no standard checkbox, 0: unchecked, 1: checked.
 };
 
 bool is_list_view(HWND window);
 ListViewRow read_list_view(HWND window);
 int list_view_index(HWND window, int *count);
+int list_view_checked(HWND window, int index);