'Looks up the new key for a blob.
Args:
old_blob_key: The original blob key.
Returns:
The blobstore.BlobKey of the migrated blob.'

@classmethod
def get_new_blob_key(cls, old_blob_key):

    record = cls.get_by_blob_key(old_blob_key)
    if record:
        return record.new_blob_ref.key()
