[ASTImporter] Changed use of Import to Import_New in ASTImporter.

Reviewers: a.sidorin, shafik, a_sidorin, martong

Reviewed By: a_sidorin

Subscribers: rnkovacs, jdoerfert, davide, aprantl, llvm-commits, gamesh411, a_sidorin, dkrupp, martong, Szelethus, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D53818

llvm-svn: 355598