The button of Accessiblity Checker Plugins is not appearing

I put Accessiblity Checker Plugin for CKEditor as modules/ckeditor/plugins/a11ychecker.
http://ckeditor.com/addon/a11ychecker

CKEditor module loads it, so I find the followings at /admin/config/content/ckeditor/edit/Advanced.

Plugin file: a11ychecker
Plugin file: balloonpanel
Plugin for inserting Drupal teaser and page breaks.

But I cannot find the button of a11ychecker in Available buttons Section.

I insert var_dump($plugins); in modules/ckeditor/includes/ckeditor.admin.inc, then I find the followings.

array(7) {
["a11ychecker"]=>
array(5) {
["name"]=>
string(11) "a11ychecker"
["desc"]=>
string(24) "Plugin file: a11ychecker"
["path"]=>
string(38) "/modules/ckeditor/plugins/a11ychecker/"
["buttons"]=>
bool(false)
["default"]=>
string(1) "f"
}
["balloonpanel"]=>
array(5) {
["name"]=>
string(12) "balloonpanel"
["desc"]=>
string(25) "Plugin file: balloonpanel"
["path"]=>
string(39) "/modules/ckeditor/plugins/balloonpanel/"
["buttons"]=>
bool(false)
["default"]=>
string(1) "f"
}
["drupalbreaks"]=>
array(5) {
["name"]=>
string(12) "drupalbreaks"
["desc"]=>
string(51) "Plugin for inserting Drupal teaser and page breaks."
["path"]=>
string(39) "/modules/ckeditor/plugins/drupalbreaks/"
["buttons"]=>
array(1) {
["DrupalBreak"]=>
array(2) {
["label"]=>
string(11) "DrupalBreak"
["icon"]=>
string(22) "images/drupalbreak.png"
}
}
["default"]=>
string(1) "t"
}
}

So, ckeditor_load_plugins function can't get a11ychecker's "label" and "icon" .

Thanks.