Switch a `promise_test` to a plain synchronous `test`

This adapts to "Reject non-thenable values" upstream:
https://github.com/web-platform-tests/wpt/pull/12898

This is blocking updating LayoutTests/resources/testharness.js.

Bug: 892613
Change-Id: Ifbc91824c0a5687a74cc6f16e02457da60dc4e85
Reviewed-on: https://chromium-review.googlesource.com/c/1264585
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597521}
1 file changed