Macro metrics_size_class

macro_rules! metrics_size_class {
    ($namespace:ident
        @size_class ($(($name:ident, $desc:expr, $metric:expr, $conv:expr)),*)
        @file ($(($f_name:ident, $f_metric:ident, $f_desc:expr)),*)
    ) => { ... };
    (@define $namespace:ident
        @size_class $(($name:ident, $desc:expr, $metric:expr, $conv:expr)),*
        @file $(($f_name:ident, $f_metric:ident, $f_desc:expr)),*
    ) => { ... };
}