Media playhead button is sometimes 1px wider: media/video-playing-and-pause.html flakey
https://bugs.webkit.org/show_bug.cgi?id=112659

* platform/mac/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146180 268f45cc-cd09-0410-ab3c-d52691b4dbfc