[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/DivZeroChecker.cpp b/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
index dcf6a86..3a68598 100644
--- a/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/DivZeroChecker.cpp
@@ -39,12 +39,8 @@
     if (!BT)
       BT.reset(new BuiltinBug("Division by zero"));
 
-    BugReport *R =
-      new BugReport(*BT, Msg, N);
-
-    bugreporter::addTrackNullOrUndefValueVisitor(N,
-                                                 bugreporter::GetDenomExpr(N),
-                                                 R);
+    BugReport *R = new BugReport(*BT, Msg, N);
+    bugreporter::trackNullOrUndefValue(N, bugreporter::GetDenomExpr(N), *R);
     C.EmitReport(R);
   }
 }