Indeed. Detached is only applicable to the ntp, but some percentage of attached is on the ntp.

NTP folks, is there a way to answer this question nowadays?

I'm not aware of any existing metrics that would capture this. Shouldn't be too hard to add though.

Who owns the (new) NTP efforts these days?

Note that this request is about desktop.

+ramyan is ramping up on Desktop NTP ownership

It looks like I'll be able to do this by checking IsInstantNTP(WebContents). 

Ah, one more thing I thought of: IsInstantNTP will not cover the Incognito and Guest Mode NTPs. I don't know if that's good or bad in this case :)

For my original use case, I would prefer if the NTP covered all possible NTPs, instant or not, incognito or not, Google default search engine or not, guest mode, etc.

If it's hard to get them all (per bug 624410), then I can be satisfied with IsInstantNTP.

Can we at least do
IsInstantNTP() || url.spec() == chrome::kChromeUINewTabURL
?
(the latter will help capture things like extension-replaced NTPs)

Also, will that second term end up including incognito?

IsInstantNTP already covers third-party NTPs. Adding the comparison to kChromeUINewTabURL will also capture Incognito and Guest. I don't know about extensions.

Making this available in case someone else has cycles to work on it in the near term. WIP crrev.com/r/908049 may have some useful comments to refer to when starting on this.