[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/UndefBranchChecker.cpp b/lib/StaticAnalyzer/Checkers/UndefBranchChecker.cpp
index 70a33c7..8a97b05 100644
--- a/lib/StaticAnalyzer/Checkers/UndefBranchChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/UndefBranchChecker.cpp
@@ -99,7 +99,7 @@
 
       // Emit the bug report.
       BugReport *R = new BugReport(*BT, BT->getDescription(), N);
-      bugreporter::addTrackNullOrUndefValueVisitor(N, Ex, R);
+      bugreporter::trackNullOrUndefValue(N, Ex, *R);
       R->addRange(Ex->getSourceRange());
       R->disablePathPruning();