Add performance test related to font fallback
https://bugs.webkit.org/show_bug.cgi?id=139332

Reviewed by Simon Fraser.

* Layout/font-fallback.html: Added.
* Layout/resources/font-fallback.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177051 268f45cc-cd09-0410-ab3c-d52691b4dbfc