Summary:
- Avoid holding lock while calling out to `send:withParams:`; it's hard to reason about whether we could trigger deadlock.
- Remove unnecessary `lastInvalidateMessage` ivar; we already ensure that we send at most one invalidate batch per 500ms by using `invalidateMessageQueued`.
- Misc code style items
Reviewed By: Andrey-Mishanin
Differential Revision: D20462193
fbshipit-source-id: 80f61e5a7ce5021e16ebc19a2ec40adfc46f9b92
89d6dfcf95