[ASTImporter] Enable disabled but passing test

Summary:
There is a test which passes since D32947, but it was forgotten to be enabled.
This patch enables that disabled test.

Reviewers: a.sidorin, r.stahl, xazax.hun

Subscribers: rnkovacs, dkrupp, cfe-commits

Differential Revision: https://reviews.llvm.org/D47069

llvm-svn: 332728

clang/unittests/AST/ASTImporterTest.cpp

@@ -1399,7 +1399,7 @@ TEST_P(ASTImporterTestBase, IDNSOrdinary) {
   EXPECT_EQ(From->getIdentifierNamespace(), To->getIdentifierNamespace());
 }
 
-TEST_P(ASTImporterTestBase, DISABLED_IDNSOfNonmemberOperator) {
+TEST_P(ASTImporterTestBase, IDNSOfNonmemberOperator) {
   Decl *FromTU = getTuDecl(
       R"(
       struct X {};