Sync web-platform-tests PR 19701 into mozilla-central (this bug is closed when the sync is complete).

PR: https://github.com/web-platform-tests/wpt/pull/19701
Details from upstream follow.

Aaron Tagliaboschi <aarontag@chromium.org> wrote:

Implement Sec-CH-UA-Mobile

Mobile is a boolean client hint that informs whether a "mobile" or
"desktop" user experience should be supplied.

Bug: 928669
Change-Id: Ia983cfa516c28b6a747b270abcc44e71ed39e1b5
Reviewed-on: https://chromium-review.googlesource.com/1829793
WPT-Export-Revision: d913a3c4ddf15e4f70604a559a6540a6f352b452

CI Results

Ran 13 Firefox configurations based on mozilla-central, and Firefox, Chrome, and Safari on GitHub CI

Total 10 tests and 2 subtests

Status Summary

Firefox

OK : 10
PASS : 8
FAIL : 8

Chrome

OK : 10
PASS : 13
FAIL : 3

Safari

OK : 9
PASS : 8
FAIL : 7
TIMEOUT: 2

Links

Gecko CI (Treeherder)
GitHub PR Head
GitHub PR Base

Details

New Tests That Don't Pass

/client-hints/accept_ch.tentative.https.html
Loading of resources/expect_client_hints_headers.html did not finish.: FAIL (Chrome: FAIL, Safari: TIMEOUT)
/client-hints/accept_ch.tentative.sub.https.html
Accept-CH header test: FAIL (Chrome: PASS, Safari: FAIL)
/client-hints/http_equiv_accept_ch.tentative.https.html
Test that the browser attaches client hints on subresources in the same navigation: FAIL (Chrome: PASS, Safari: FAIL)
Loading of resources/expect_client_hints_headers.html did not finish.: FAIL (Chrome: FAIL, Safari: FAIL)
/client-hints/accept_ch_feature_policy.tentative.sub.https.html
Accept-CH header test: FAIL (Chrome: FAIL, Safari: FAIL)
Cross-Origin Accept-CH header test: FAIL (Chrome: PASS, Safari: FAIL)
/client-hints/accept_ch_no_feature_policy.tentative.sub.https.html
Accept-CH header test: FAIL (Chrome: PASS, Safari: FAIL)
/client-hints/http_equiv_accept_ch.tentative.sub.https.html
Same origin Accept-CH http-equiv test: FAIL (Chrome: PASS, Safari: FAIL)

https://hg.mozilla.org/mozilla-central/rev/a75eb2975461