GitLab

The following tests are converted to use testharness.js
from js-test.js in LayoutTests/shadow-dom/.

* attach-shadow-with-parameter.html
* focus-slide-on-shadow-host.html
* focus-shadowhost-display-none.html

For attach-shadow-with-parameter.html, I added some return
value checks, but otherwise almost straightforward conversion
to testharness.js API.

Review-Url: https://codereview.chromium.org/2333623003
Cr-Commit-Position: refs/heads/master@{#418770}