Summary:
Ievgen ran into this bug with his dper work - we didn't preserve metadata on lengths field.
Also, we didn't take keep_blobs into account for List's main field. Now fixed.
Also, reformat the file to be nice.
Differential Revision: D4357859
fbshipit-source-id: 1c26c533a10d38afab13b46ccbcb541f5fa9074a