[Static Analyzer] Generics Checker: When an ObjC method returns a specialized object, track it properly.

Differential Revision: http://reviews.llvm.org/D12889



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@247861 91177308-0d34-0410-b5e6-96231b3b80d8