unmount method
Unmounts a file system with the given fileSystemId. It
must be called after onUnmountRequested is invoked. Also,
the providing extension can decide to perform unmounting if not requested
(eg. in case of lost connection, or a file error).
In case of an error, runtime.lastError will be set with a
corresponding error code.
Implementation
Future<void> unmount(UnmountOptions options) async {
await promiseToFuture<void>(
$js.chrome.fileSystemProvider.unmount(options.toJS));
}