<rdar://problem/9484496> REGRESSION (WebKit2): Checkboxes and radio buttons are drawn...

<rdar://problem/9484496> REGRESSION (WebKit2): Checkboxes and radio buttons are drawn 1 pixel too high, not repainted properly
https://bugs.webkit.org/show_bug.cgi?id=69727

Reviewed by Anders Carlsson.

* platform/mac/ThemeMac.mm: Made WebCoreFlippedView an NSControl subclass so that the NSButtonCell
used to draw checkboxes and radio buttons can make it its controlView, and consequently check and
obey its flippedness.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@97032 268f45cc-cd09-0410-ab3c-d52691b4dbfc