[analyzer] Rename addTrackNullOrUndefValueVisitor to trackNullOrUndefValue.

This helper function (in the clang::ento::bugreporter namespace) may add more
than one visitor, but conceptually it's tracking a single use of a null or
undefined value and should do so as best it can.

Also, the BugReport parameter has been made a reference to underscore that
it is non-optional.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162720 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp b/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
index c582cfc..f809a0d 100644
--- a/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/AttrNonNullChecker.cpp
@@ -105,7 +105,7 @@
         // Highlight the range of the argument that was null.
         R->addRange(Call.getArgSourceRange(idx));
         if (const Expr *ArgE = Call.getArgExpr(idx))
-          bugreporter::addTrackNullOrUndefValueVisitor(errorNode, ArgE, R);
+          bugreporter::trackNullOrUndefValue(errorNode, ArgE, *R);
         // Emit the bug report.
         C.EmitReport(R);
       }