Migrate WTF::HashSet::add() to ::insert() [part 1 of N]

third_party/WebKit/Source/core/xml/XPathPath.cpp

Index: third_party/WebKit/Source/core/xml/XPathPath.cpp
diff --git a/third_party/WebKit/Source/core/xml/XPathPath.cpp b/third_party/WebKit/Source/core/xml/XPathPath.cpp
index 52cd1f95af5f1a74e2f7b49009fd938a30c01a1b..6960e729077ab451ddae8d9b7ab1fbb0cf1d07f1 100644
--- a/third_party/WebKit/Source/core/xml/XPathPath.cpp
+++ b/third_party/WebKit/Source/core/xml/XPathPath.cpp
@@ -145,7 +145,8 @@ void LocationPath::evaluate(EvaluationContext& context, NodeSet& nodes) const {
         resultIsSorted = false;
 
       for (const auto& node : *matches) {
-        if (!needToCheckForDuplicateNodes || newNodesSet.add(node).isNewEntry)
+        if (!needToCheckForDuplicateNodes ||
+            newNodesSet.insert(node).isNewEntry)
           newNodes->append(node);
       }
     }