This doesn't work with TinyMCE 5.

file_browser_callback was removed in version 5. The code to get the dialog box to display would be:

        file_picker_callback: function(callback, value, meta) {
            // trigger file upload form
            if (meta.filetype == 'image') {
                $('#formUpload input').click();
            }
        }

However, the javascript returned to fill in the dialog box isn't working. Laravel returns it, but it does nothing (probably due to how they changed the dialog box). I'm going to work on it and see if I can figure it out, but my javascript isn't strong, so it may take a while.