The backend's cancel scan result. If the result is
OperationResult.SUCCESS or
OperationResult.CANCELLED, the scan has been cancelled and
the scanner is ready to start a new scan. If the result is
OperationResult.DEVICE_BUSY , the scanner is still
processing the requested cancellation; the caller should wait a short
time and try the request again. Other result values indicate a permanent
error that should not be retried.