the #GFile where the current web page should be saved to.
the #WebKitSaveMode specifying how the web page should be saved.
a #GCancellable or %NULL to ignore
a #GAsyncReadyCallback to call when the request is satisfied
the data to pass to callback function
Asynchronously save the current web page associated to the #WebKitWebView into a self-contained format using the mode specified in @save_mode and writing it to @file.
When the operation is finished, @callback will be called. You can then call webkit_web_view_save_to_file_finish() to get the result of the operation.