[Existing implementation](https://github.com/GoogleCloudPlatform/gcloud-python/blob/56daf8c248be400f69e8c292743a897ea83c34cb/gcloud/storage/exceptions.py#L158) [where we would use it](https://github.com/GoogleCloudPlatform/gcloud-python/pull/506#discussion_r22629787)