Summary: Depends on D19131. Ref T13088. During log finalization, stream the log into Files to support "Download Log", archive to Files, and API access.
Test Plan: Ran `write-log` and `rebuild-log`, saw Files objects generate with log content and appropriate permissions.
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13088
Differential Revision: https://secure.phabricator.com/D19132
