Modify checkLayout to receive the log container as an optional parameter
https://bugs.webkit.org/show_bug.cgi?id=112793

Reviewed by Darin Adler.

Add a way to specify the container manually for checkLayout. This is helpful to measure regions for nested
named flows (and probably other cases as well).

* resources/check-layout.js: Added an optional parameter to window.checkLayout.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150067 268f45cc-cd09-0410-ab3c-d52691b4dbfc