[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/UndefResultChecker.cpp b/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
index e220499..605f677 100644
--- a/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
@@ -76,10 +76,10 @@
     BugReport *report = new BugReport(*BT, OS.str(), N);
     if (Ex) {
       report->addRange(Ex->getSourceRange());
-      bugreporter::addTrackNullOrUndefValueVisitor(N, Ex, report);
+      bugreporter::trackNullOrUndefValue(N, Ex, *report);
     }
     else
-      bugreporter::addTrackNullOrUndefValueVisitor(N, B, report);
+      bugreporter::trackNullOrUndefValue(N, B, *report);
     
     report->disablePathPruning();
     C.EmitReport(report);