pub unsafe extern "C" fn webkit_user_style_sheet_new(
    source: *const c_char,
    injected_frames: WebKitUserContentInjectedFrames,
    level: WebKitUserStyleLevel,
    allow_list: *const *const c_char,
    block_list: *const *const c_char
) -> *mut WebKitUserStyleSheet
Available on crate feature v2_6 only.