Summary:
The content inset of a collection view can change at any time (as it does with our refresh control) and isn't a good measure of the container size. I don't want to totally remove that API though, so I changed the default behavior, added an insets API, and also added the functionality of the original in a new API.
This makes sizes much more deterministic.
Reviewed By: jessesquires
Differential Revision: D4800758
fbshipit-source-id: 85ce843b5b1c297cea2e2ea705fa255617cbe356