Implement versioned drafts in EditEngine comment forms
Summary:
Ref T9132. Fixes T5031. This approximately implements the plan described in T5031#67988:
When we recieve a preview request, don't write a draft if the form is from a version of the object before the last update the viewer made.
This should fix the race-related (?) zombie draft comments that sometimes show up.
I just added a new object for this stuff to make it easier to do stacked actions (or whatever we end up with) a little later, since I needed to do some schema adjustments anyway.
Test Plan:
- Typed some text.
- Reloaded page.
- Draft stayed there.
- Tried real hard to get it to ghost by submitting stuff in multiple windows and typing a lot and couldn't, although I didn't bother specifically narrowing down the race condition.
Reviewers: chad
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D14640