[clang] [WebKit checkers] Recognize NS_RETURNS_RETAINED and CF_RETURNS_RETAINED. (PR #157629)

[Rashmi Mudduluru via cfe-commits]

https://github.com/t-rasmud approved this pull request.

I left a small nit in the test case. Otherwise, LGTM!

https://github.com/llvm/llvm-project/pull/157629