Introduce HasHTMLTagName functor and use it with ElementTraversal

Source/core/html/HTMLElement.h

Index: Source/core/html/HTMLElement.h
diff --git a/Source/core/html/HTMLElement.h b/Source/core/html/HTMLElement.h
index 590b8eff543b5b1692d5a03681e742c48e930649..082ca218edb6a9674ca8c24bd6baee87f78fd74e 100644
--- a/Source/core/html/HTMLElement.h
+++ b/Source/core/html/HTMLElement.h
@@ -149,6 +149,15 @@ inline bool Node::hasTagName(const HTMLQualifiedName& name) const
     return isHTMLElement() && toHTMLElement(*this).hasTagName(name);
 }
 
+// Functor used to match HTMLElements with a specific HTML tag when using the ElementTraversal API.
+class HasHTMLTagName {
+public:
+    explicit HasHTMLTagName(const HTMLQualifiedName& tagName): m_tagName(tagName) { }
+    bool operator() (const HTMLElement& element) const { return element.hasTagName(m_tagName); }
+private:
+    const HTMLQualifiedName& m_tagName;
+};
+
 // This requires isHTML*Element(const Element&) and isHTML*Element(const HTMLElement&).
 // When the input element is an HTMLElement, we don't need to check the namespace URI, just the local name.
 #define DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(thisType) \