cryptographicallyRandomValuesFromOS should use CCRandomCopyBytes when available.

cryptographicallyRandomValuesFromOS should use CCRandomCopyBytes when available.
https://bugs.webkit.org/show_bug.cgi?id=148439

Reviewed by Alexey Proskuryakov.

Recently, we switched to using arc4random_buf on Darwin but further research indicates that
arc4random_buf has the same behavior we had before and thus we were just pushing the problem
further down the stack. CCRandomCopyBytes, however, appears to be more advanced and has much
better error handling than we had before.

* WTF.xcodeproj/project.pbxproj:
* wtf/OSRandomSource.cpp:
(WTF::cryptographicallyRandomValuesFromOS):
* wtf/spi/darwin/CommonCryptoSPI.h: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189633 268f45cc-cd09-0410-ab3c-d52691b4dbfc