Compositing tests failing after http://trac.webkit.org/changeset/147502
https://bugs.webkit.org/show_bug.cgi?id=113838

Temporarily marking as failing.

* platform/mac/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147510 268f45cc-cd09-0410-ab3c-d52691b4dbfc