[Shadow] LargeDistributionWithLayout.html should be updated

[Shadow] LargeDistributionWithLayout.html should be updated
https://bugs.webkit.org/show_bug.cgi?id=105242

Reviewed by Ryosuke Niwa.

Since this test was written when distribution took O(N^2). However, now it's almost O(N), so this test finishes
in very short time. We should convert it unit to runs/s.

This test contains a some error to cause test failure, e.g. using obsolete API, so they also should be fixed.

* ShadowDOM/LargeDistributionWithLayout.html:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@137990 268f45cc-cd09-0410-ab3c-d52691b4dbfc