Chromium uses gtk_file_chooser_set_current_folder in several places in select_file_dialog_impl_gtk.cc, however the docs[1] suggest that way of doing things is no longer recommended:

"Note that old versions of the file chooser’s documentation suggested using gtk_file_chooser_set_current_folder() in various situations, with the intention of letting the application suggest a reasonable default folder. This is no longer considered to be a good policy, as now the file chooser is able to make good suggestions on its own."

[1] https://developer.gnome.org/gtk3/stable/GtkFileChooserDialog.html#gtkfilechooserdialog-setting-up