Remove checks for NULL before g_free() and g_clear_object(). Merge check for NULL, freeing of pointer and its setting to NULL by g_clear_pointer(). https://bugzilla.gnome.org/show_bug.cgi?id=733157
The stock browser was removed from gtk3-demo.
It was a failed experiment, it is basically unused, and it complicates code in GtkIconTheme that we want to rework.