Chrome 110 applies User-Agent reduction to Navigator properties + User-Agent header

[chrisdavidmills]

Summary

Chromium browsers support User-Agent reduction, which means that features such as the User-Agent HTTP header provide less-specific information in an effort to reduce their effectiveness for fingerprinting/tracking.

This PR adds data points covering User-Agent reduction to relevant web platform features that I know to be affected by the change.

Compat data sources:

• From looking at https://blog.chromium.org/2021/09/user-agent-reduction-origin-trial-and-dates.html, it looks like rollout of UA reduction to 100% of Chromium desktop users occurred in version 110, while the version was 113 for Chromium Android users. I asked @miketaylr about this, and he confirmed it to be correct.
• From looking at https://www.chromium.org/updates/ua-reduction/#applicable-platforms, it looks like Android WebView should be false

Another question for Mike: For all of these data points, I used https://wicg.github.io/ua-client-hints/#user-agent as the spec_url. Are there better spec URLs we can point to for these individual features?

This PR is part of the final set of privacy sandbox information to be added to MDN. Much of it is being removed, but this feature is stable and will be kept, so it should be added.

Test results and supporting details

Related issues

[github-actions]

Tip: Review these changes grouped by change (recommended for most PRs), or grouped by feature (for large PRs).

[miketaylr]

From looking at https://www.chromium.org/updates/ua-reduction/#applicable-platforms, it looks like Android WebView should be false

That's correct, but we're trying to ship it in the future.

Another question for Mike: For all of these data points, I used https://wicg.github.io/ua-client-hints/#user-agent as the spec_url. Are there better spec URLs we can point to for these individual features?

I'd use https://compat.spec.whatwg.org/#ua-string-section

[chrisdavidmills]

From looking at https://www.chromium.org/updates/ua-reduction/#applicable-platforms, it looks like Android WebView should be false

That's correct, but we're trying to ship it in the future.

This is fine. We can follow up with another PR when it ships.

Another question for Mike: For all of these data points, I used https://wicg.github.io/ua-client-hints/#user-agent as the spec_url. Are there better spec URLs we can point to for these individual features?

I'd use https://compat.spec.whatwg.org/#ua-string-section

Great, thanks. I've updated it in the latest commit.

[miketaylr]

non-owner LGTM

[caugner]

Here's my suggestion, but before applying, I'd like to get a second opinion by @ddbeck, who might have a better idea.

Suggested change

	"User-Agent_reduction": {
	"__compat": {
	"description": "Provides limited information due to [User-agent](https://developer.mozilla.org/docs/Web/HTTP/Guides/User-agent_reduction) reduction.",
	"applies_UA_reduction": {
	"__compat": {
	"description": "Applies [User-agent reduction](https://developer.mozilla.org/docs/Web/HTTP/Guides/User-agent_reduction)",

[chrisdavidmills]

FWIW, this sounds good to me.