Simplify EventLoop::cycle() on Mac.

https://webkit.org/b/116392

Reviewed by Anders Carlsson.

* platform/mac/EventLoopMac.mm:
(WebCore::EventLoop::cycle): Use CFRunLoopRunInMode instead.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150339 268f45cc-cd09-0410-ab3c-d52691b4dbfc