Cancels the request. This will cause isComplete to return true once the cancellation has been processed, but AsyncOperationResponse.wasSuccessful will return false (unless it completed before the cancellation was processed, in which case it is still allowed to finish successfully).

After cancelling a request, you should still wait for it to complete to ensure that the task has actually released its resources before doing anything else on it.

Once a cancellation request has been sent, it cannot be undone.