R1:129e3a120849

Fix a minor/harmless race with feed publishers in certain draft states

Summary:
Depends on D18851. Ref T13035. After D18819, revision creation transactions may be split into two groups (if prototypes are enabled).

This split means we have two workers. The first worker doesn't publish feed stories or mail; the second one does.

Currently, both workers call `shouldPublishFeedStory()` before they queue, and then again after the daemons pull them out of the queue. However, the answer to this question can…