Flow was having a hard time realizing that ChatNavigationProp (definition) and TabNavigationProp (definition) are valid NavigationProps (definition, relevant line).
This diff allows us to convince Flow by providing all type params of NavigationProp at the getParent invocation.
Depends on D9988
I actually think this is a bit too small. But that's what's in the design.
https://www.figma.com/file/L675ETKDnGaSwlpZAw4MIC/Mobile-App?node-id=351%3A455
@ashoat - I think 16px looks better.