WordPress - functions.php: Add custom images sizes to dropdown media menu

wordpress.add-custom-image-sizes-to-menu.php

//  Add custom image sizes
add_image_size( 'icon', 40, 40, true );
add_image_size( 'icon2x', 80, 80, true );

add_filter('image_size_names_choose', 'my_image_sizes');
function my_image_sizes($sizes) {
    $addsizes = array(
        "icon" => __( "Icon"),
        "icon2x" => __( "Icon@2x")
    );
    $newsizes = array_merge($sizes, $addsizes);
    return $newsizes;
}