Syncing wpt PR 31391 found new untriaged test failures in CI

Tests Affected

New Tests That Don't Pass

/css/css-cascade/layer-statement-before-import.html: ERROR (Chrome: OK, Safari: ERROR)

CI Results

Gecko CI (Treeherder)
GitHub PR Head

Notes

These updates will be on mozilla-central once bug 1737930 lands.

Note: this bug is for tracking fixing the issues and is not
owned by the wpt sync bot.

This bug is linked to the relevant tests by an annotation in
https://github.com/web-platform-tests/wpt-metadata. These annotations
can be edited using the wpt interop dashboard
https://jgraham.github.io/wptdash/

If this bug is split into multiple bugs, please also update the
annotations, otherwise we are unable to track which wpt issues are
already triaged. Resolving as duplicate or closing this issue should
be cause the bot to automatically update or remove the annotation.

From the failure log;
[task 2021-10-28T18:15:15.408Z] 18:15:15 INFO - PID 1273 | JavaScript error: http://web-platform.test:8000/css/css-cascade/layer-statement-before-import.html, line 170: TypeError: Illegal constructor.

Probably

sheet = new CSSStyleSheet();

This line.