Consistently use ElementTraversal API when looking for an Element

Source/core/dom/Node.cpp

Index: Source/core/dom/Node.cpp
diff --git a/Source/core/dom/Node.cpp b/Source/core/dom/Node.cpp
index 1671ca9b37c28770438f50fe740663bdc7048343..0623975c6ac9cafdefc013ea77129692341cf520 100644
--- a/Source/core/dom/Node.cpp
+++ b/Source/core/dom/Node.cpp
@@ -2471,9 +2471,9 @@ void Node::unregisterScopedHTMLStyleChild()
 size_t Node::numberOfScopedHTMLStyleChildren() const
 {
     size_t count = 0;
-    for (Node* child = firstChild(); child; child = child->nextSibling()) {
+    for (Element* child = ElementTraversal::firstWithin(*this); child; child = ElementTraversal::nextSibling(*child)) {
         if (child->hasTagName(HTMLNames::styleTag) && toHTMLStyleElement(child)->isRegisteredAsScoped())
-            count++;
+            ++count;
     }
 
     return count;