Use new is*Element() helper functions more in core/ code

Source/core/xml/parser/XMLDocumentParser.cpp

Index: Source/core/xml/parser/XMLDocumentParser.cpp
diff --git a/Source/core/xml/parser/XMLDocumentParser.cpp b/Source/core/xml/parser/XMLDocumentParser.cpp
index c2a06b2a0c3401e4498807e6c9e81e54e5b145b7..5824e2bbdcafe0b5e7c389d75ebb5f8ae6fd5ae5 100644
--- a/Source/core/xml/parser/XMLDocumentParser.cpp
+++ b/Source/core/xml/parser/XMLDocumentParser.cpp
@@ -1010,13 +1010,13 @@ void XMLDocumentParser::startElementNs(const AtomicString& localName, const Atom
 
     m_currentNode->parserAppendChild(newElement.get());
 
-    if (newElement->hasTagName(HTMLNames::templateTag))
-        pushCurrentNode(toHTMLTemplateElement(newElement.get())->content());
+    if (isHTMLTemplateElement(*newElement))
+        pushCurrentNode(toHTMLTemplateElement(*newElement).content());
     else
         pushCurrentNode(newElement.get());
 
-    if (newElement->hasTagName(HTMLNames::htmlTag))
-        toHTMLHtmlElement(newElement)->insertedByParser();
+    if (isHTMLHtmlElement(*newElement))
+        toHTMLHtmlElement(*newElement).insertedByParser();
 
     if (!m_parsingFragment && isFirstElement && document()->frame())
         document()->frame()->loader().dispatchDocumentElementAvailable();