Function webkit2gtk_sys::webkit_web_view_load_bytes

pub unsafe extern "C" fn webkit_web_view_load_bytes(
    web_view: *mut WebKitWebView, 
    bytes: *mut GBytes, 
    mime_type: *const c_char, 
    encoding: *const c_char, 
    base_uri: *const c_char
)

This is supported on crate feature v2_6 only.