iOS build fix.

* UIProcess/mac/WKPreviewPopoverAnimationController.mm:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177565 268f45cc-cd09-0410-ab3c-d52691b4dbfc
dispatch to main thread before accessing playerController() in WebVideoFullscreenInterfaceAVKit::setCanPlayFastReverse
https://bugs.webkit.org/show_bug.cgi?id=139809

Patch by Jeremy Jones <jeremyj@apple.com> on 2014-12-18
Reviewed by Dan Bernstein.

This prevents a race in playerController().

* platform/ios/WebVideoFullscreenInterfaceAVKit.mm:
(WebVideoFullscreenInterfaceAVKit::setCanPlayFastReverse):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177566 268f45cc-cd09-0410-ab3c-d52691b4dbfc