onReceivedError()
Report web resource loading error to the host application. These errors usually indicate inability to connect to the server.
It's about network/server errors. The errors are not HTTP errors but are
unrecoverable resource errors (file not found, no network connection, server not found for the main resource,
etc.). If there is a network error, there cannot be a HTTP error code transmitted.
onReceivedHttpError()
Notify the host application that an HTTP error has been received from the server while loading a resource. HTTP errors have status codes >= 400.