I put Blink>Input becuase input-dev-related people have been working on viewport issues. Is there a better component?

While I agree in principle but I think we'd need to be careful. Screen coordinates are sometimes used for things like gesture detection and eye tracking; there are some niche use cases that we can't break. It looks like window.screenX|Y are used on ~3% of page loads (https://www.chromestatus.com/metrics/feature/popularity) so this change has the potential to affect a large number of pages.

I'll leave it open on input-dev but I don't see us prioritizing this any time soon unless there's an urgent, concrete reason.

I did a quick query with BigQuery:

SELECT url
FROM [httparchive:har.2016_08_01_chrome_requests_bodies]
WHERE body CONTAINS 'window.screenX'
GROUP BY url
ORDER BY url
LIMIT 2000

It looks like the vast majority of uses contributing to the 3% are pop-up / pop-under ad libraries. The next popular users are "crayon-syntax-highlighter" (a Word Press plugin) and a library for federated logins with social networks (oneall.com, also doing popups).

Yah, I suspect we could probably do it without causing much havoc. I just checked Firefox and they still return the actual screen values too; I'm guessing other browsers do as well. If this does happen, I'd like to see other vendors at least commit to doing it too.

See also:
* https://bugs.webkit.org/show_bug.cgi?id=161227
* https://twitter.com/smfr/status/769006160602988545
* https://bugzilla.mozilla.org/show_bug.cgi?id=1298116

> Screen coordinates are sometimes used for things like gesture detection and eye tracking

Are either of those Web-exposed though?

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I agree with bokan@ that this feature seems reasonable as long as we don't break a huge amount of usecases.
Reporter are there any other similar privacy related fields that we need to take care of and you might know?

For CSSOM View, the only additional relevant fields I'm aware of are:
    MouseEvent.screen{X,Y}
though I don't claim expertise in this area.
The CSSOM View spec unfortunately lacks a "Privacy & Security Considerations" section currently,
which could offer more guidance here. Adding such a section falls within https://github.com/w3c/csswg-drafts/issues/207

The suggested changes also have implications for
https://drafts.csswg.org/cssom-view/#the-features-argument-to-the-open()-method
but that's more a matter of making the more-private model of these fields work consistently.
I'm not aware of open() itself leaking any screen/window info.

So to recap, all the known-relevant fields are:
window.screen{X,Y}
MouseEvent.screen{X,Y}
window.screen.{width,height}
window.screen.avail{Width,Height}

 Issue 356113  has been merged into this issue.