Have ElementTraversal / NodeTraversal's next() methods take a reference

Source/core/css/StyleInvalidationAnalysis.cpp

Index: Source/core/css/StyleInvalidationAnalysis.cpp
diff --git a/Source/core/css/StyleInvalidationAnalysis.cpp b/Source/core/css/StyleInvalidationAnalysis.cpp
index b0053cb64e92f05ec0d5ee0d934b6e2ad697408b..9fe923eb3e55d7743f4198a9b66b8f66cdd62a07 100644
--- a/Source/core/css/StyleInvalidationAnalysis.cpp
+++ b/Source/core/css/StyleInvalidationAnalysis.cpp
@@ -223,7 +223,7 @@ void StyleInvalidationAnalysis::invalidateStyle(Document* document)
             element = ElementTraversal::nextSkippingChildren(element);
             continue;
         }
-        element = ElementTraversal::next(element);
+        element = ElementTraversal::next(*element);
     }
 }