[Shadow] Performance tests of distribution for changing select attribute

[Shadow] Performance tests of distribution for changing select attribute
https://bugs.webkit.org/show_bug.cgi?id=103611

Reviewed by Hajime Morita.

We would like to measure ShadowDOM performance and compare it to the similar functional HTML without using ShadowDOM.
In this patch, we add a case when select attribute of HTMLContentElement is changed.

* ShadowDOM/ChangingSelect.html: Added.
* ShadowDOM/ChangingSelectWithoutShadow.html: Added.
* Skipped:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@136120 268f45cc-cd09-0410-ab3c-d52691b4dbfc