After setting GOBJECT_DEBUG=objects comparing the outputs                  
of the following program run with ITERATIONS set to 2 and 1:               

#include <gtk/gtk.h>

#ifndef ITERATIONS 
#define ITERATIONS 2
#endif

int
main (int   argc,  
      char *argv[])
{
  int i;

  if (gtk_init_check (&argc, &argv))
    for (i = 0; i < ITERATIONS; ++i)
      {
        GtkWidget *dialog = gtk_file_chooser_dialog_new ("Open File", NULL,
                                                         GTK_FILE_CHOOSER_ACTION_OPEN,
                                                         "Cancel", GTK_RESPONSE_CANCEL,
                                                         NULL);            
        gtk_dialog_run (GTK_DIALOG (dialog));
        gtk_widget_destroy (dialog);                                       
      }

  return 0;
}


the number of objects alive at exit increases for the presence             
of a GDaemonFileEnumerator.

The object is created here:

https://git.gnome.org/browse/gtk+/tree/gtk/gtkplacesview.c?h=gtk-3-22#n994

Comparing the file_enumerator API usage in gtk/gtkfilesystemmodel.c

https://git.gnome.org/browse/gtk+/tree/gtk/gtkfilesystemmodel.c?h=gtk-3-22#n1282

it seems that 'enumerator' should be unreffed after the call to
g_file_enumerator_next_files_async

https://git.gnome.org/browse/gtk+/tree/gtk/gtkplacesview.c?h=gtk-3-22#n1014