[Mac] Flaky crash in SliderThumbElement::defaultEventHandler on fast/forms/range/slider-delete-while-dragging-thumb.html
https://bugs.webkit.org/show_bug.cgi?id=108223

* platform/mac/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146217 268f45cc-cd09-0410-ab3c-d52691b4dbfc