Reland "[AST] Traverse the class type loc inside the member type loc.""

Summary: added a unittest which causes "TL.getClassTInfo" is null.

Reviewers: ilya-biryukov

Subscribers: mgorny, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D71186