Summary:
See D4812.
- This preference disables the file tree completely.
- It defaults off, so users who want it will have to go turn it on.
- Maybe slightly cleaner would be doing this if the tree was hidden and then ajaxing it in if you press "F", but that's complicated and I don't want to bother.
- Generally, I think this element is useful to something like 5% of users and not useful to 95%.
Test Plan: Enabled and disabled file tree. Looked at commits and revisions; verified they reflected the setting correctly.
Reviewers: vrana
Reviewed By: vrana
CC: aran
Differential Revision: https://secure.phabricator.com/D4813
