Asynchronously save the current web page.
Asynchronously save the current web page associated to the WebView into a self-contained
format using the mode specified in save_mode.
When the operation is finished, callback will be called. You can then call save.end to get the
result of the operation.
| this |
a WebView |
| save_mode |
the SaveMode specifying how the web page should be saved. |
| cancellable |
a Cancellable or null to ignore |
| callback |
a TaskReadyCallback to call when the request is satisfied |
| user_data |
the data to pass to callback function |