R1:d5925ffc5779

When a file is stored as chunks, show "Format: Chunks" instead of "Format: Raw"

Summary: Fixes T11712. This is somewhat misleading with encryption enabled.

Test Plan: Viewed chunked and unchunked files.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11712

Differential Revision: https://secure.phabricator.com/D16636