GitLab

This moves them from js-test to testharness and does some substantial
cleanup of asynchronous logic at the same time.

This is in preparation to move the tests into wpt_internal and use Mojo
JS modules.

Bug: 1004256
Change-Id: I47a53d3e88d777158c9ad1a65bf0500284abcb5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2639871Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#845999}