Reflected video elements hit assertion
https://bugs.webkit.org/show_bug.cgi?id=112490

Disable reflections on video again, since there's some bad behavior
caused by an underlying system framework.

* platform/graphics/ca/mac/PlatformCALayerMac.mm:
(PlatformCALayer::clone):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146001 268f45cc-cd09-0410-ab3c-d52691b4dbfc