Port Node's previousElementSibling() / nextElementSibling() to ElementTraversal

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 452ee77862f85014bc01b7558ce192e858fbfef5..471577f06159f47e58a44e98ef4201a4fa2d0b5d 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1378,7 +1378,7 @@ void Document::removeTitle(Element* titleElement)
     // FIXME: This is broken for SVG.
     // Update title based on first title element in the head, if one exists.
     if (HTMLElement* headElement = head()) {
-        for (Element* element = headElement->firstElementChild(); element; element = element->nextElementSibling()) {
+        for (Element* element = ElementTraversal::firstWithin(*headElement); element; element = ElementTraversal::nextSibling(*element)) {
             if (!element->hasTagName(titleTag))
                 continue;
             HTMLTitleElement* title = toHTMLTitleElement(element);