Sync web-platform-tests PR 25410 into mozilla-central (this bug is closed when the sync is complete).

PR: https://github.com/web-platform-tests/wpt/pull/25410
Details from upstream follow.

b'Ana SollanoKim <ansollan@microsoft.com>' wrote:

[LayoutNG] Small legend large border and large legend small border

Added two web tests:

1. Small legend large border: At this time, the legend is treated as
   monolithic and the borders are not breaking as well. As a result, the
   border goes past the fragmentation line in the first and last columns.
2. Large legend small border: Similarly, the legend goes past the
   fragmentation line in the first column. The fieldset breaks when it
   reaches the fragmentation line in the second column.

Deleted the update of the border block start value as it's no longer
useful to calculate new offsets in the fieldset.

Bug: 829028
Change-Id: I1746c9da67372f4a42ab7ab8c4184460814f486d
Reviewed-on: https://chromium-review.googlesource.com/2391217
WPT-Export-Revision: 9c2d85af30edf8d417c7d4ccb115d1f88f7e1ba2

CI Results

Ran 12 Firefox configurations based on mozilla-central, and Firefox, Chrome, and Safari on GitHub CI

Total 2 tests

Status Summary

Firefox

FAIL: 2

Chrome

FAIL: 2

Safari

FAIL: 2

Links

Gecko CI (Treeherder)
GitHub PR Head
GitHub PR Base

Details

New Tests That Don't Pass

/css/css-break/fieldset-003.html: FAIL (Chrome: FAIL, Safari: FAIL)
/css/css-break/fieldset-004.html: FAIL (Chrome: FAIL, Safari: FAIL)