Ckeditor add force download option in dialog

CKEDITOR.on( 'dialogDefinition', function( evt ) {
   var dialog = evt.data;

   if ( dialog.name == 'link' ) {
       // Get dialog definition.
       var def = evt.data.definition;         
       // Add some stuff to definition.
       
       
       
       var infoTab = def.getContents( 'info' );
       
       infoTab.add( {
type: 'checkbox',
id: 'download',
requiredContent: 'a[download]',
label: "Force Download",
setup: function( data ) {
if ( data.download !== undefined )
this.setValue( 'checked', 'checked' );
},
commit: function( data ) {
if ( this.getValue() ) {
data.download = this.getValue();
}
}
});

   }
} );

CKEDITOR.replace( 'editor' );