How to Add new Arguments to custom Control of customizer wordpress?

If you check out the source of WP_Customize_Control::__construct:

public function __construct( $manager, $id, $args = array() ) {
    $keys = array_keys( get_object_vars( $this ) );
    foreach ( $keys as $key ) {
        if ( isset( $args[ $key ] ) ) {
            $this->$key = $args[ $key ];
        }
    }

    // [redacted]
 }

So you can see, in order for it pick up your custom arguments, they need to be declared as properties of your custom class:

class WP_Customize_Foo_Control extends WP_Customize_Control {
    public $foo;
    public $moo;
}