[ASTImporter] Use llvm::Expected and Error in the importer API

Summary:
This is the final phase of the refactoring towards using llvm::Expected
and llvm::Error in the ASTImporter API.
This involves the following:
- remove old Import functions which returned with a pointer,
- use the Import_New functions (which return with Err or Expected) everywhere
  and handle their return value
- rename Import_New functions to Import
This affects both Clang and LLDB.

Reviewers: shafik, teemperor, aprantl, a_sidorin, balazske, a.sidorin

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits, lldb-commits

Tags: #clang, #lldb

Differential Revision: https://reviews.llvm.org/D61438

llvm-svn: 360760
diff --git a/clang/lib/CrossTU/CrossTranslationUnit.cpp b/clang/lib/CrossTU/CrossTranslationUnit.cpp
index 9b68f37..f504082 100644
--- a/clang/lib/CrossTU/CrossTranslationUnit.cpp
+++ b/clang/lib/CrossTU/CrossTranslationUnit.cpp
@@ -398,7 +398,7 @@
   assert(hasBodyOrInit(D) && "Decls to be imported should have body or init.");
 
   ASTImporter &Importer = getOrCreateASTImporter(D->getASTContext());
-  auto ToDeclOrError = Importer.Import_New(D);
+  auto ToDeclOrError = Importer.Import(D);
   if (!ToDeclOrError) {
     handleAllErrors(ToDeclOrError.takeError(),
                     [&](const ImportError &IE) {