Now that I think about it, I'm not sure it makes any sense to record these. Sync doesn't record each component of the redirect chain as a separate entry; instead it stores the entire chain in the navigation_redirect field:
https://cs.chromium.org/chromium/src/components/sync/protocol/session_specifics.proto?l=143

This means the qualifiers aren't meaningful; every synced navigation is both the start and end of a chain, since it always encompasses the entire chain.

Instead, I think we should just remove the qualifiers entirely. If someone is interested in whether or not there were redirects, they can check the size of the navigation_redirect field. Nicolas, any thoughts?

So, redirects will be captured by the redirect_type field, correct? Yeah, in that case we're already encoding chain start and end in a sequence of navigations. We should probably just deprecate these two fields.

FWIW, redirect_type seems to only be populated for client redirects from my ad-hoc testing. It's also a singular value, whereas the chain is of arbitrary length. 

Digging into the context for why navigation_redirect was added in the first place, I think if we wanted to augment redirect data, we'd want to add additional fields to navigation_redirect specifying each redirect_type and status code as opposed to populating singular fields for the navigation entry.  

I will re-purpose this bug to be for deprecating these fields.