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

Source/core/editing/InsertListCommand.cpp

Index: Source/core/editing/InsertListCommand.cpp
diff --git a/Source/core/editing/InsertListCommand.cpp b/Source/core/editing/InsertListCommand.cpp
index df9cb378959c13b2bc5e9afe24d067c4a0ae7413..6de0c13ab2d15d5181f054b843e3213b97ec8f87 100644
--- a/Source/core/editing/InsertListCommand.cpp
+++ b/Source/core/editing/InsertListCommand.cpp
@@ -262,7 +262,8 @@ void InsertListCommand::unlistifyParagraph(const VisiblePosition& originalStart,
     Node* previousListChild;
     VisiblePosition start;
     VisiblePosition end;
-    if (listChildNode->hasTagName(liTag)) {
+    ASSERT(listChildNode);
+    if (isHTMLLIElement(*listChildNode)) {
         start = VisiblePosition(firstPositionInNode(listChildNode));
         end = VisiblePosition(lastPositionInNode(listChildNode));
         nextListChild = listChildNode->nextSibling();
@@ -374,7 +375,7 @@ PassRefPtr<HTMLElement> InsertListCommand::listifyParagraph(const VisiblePositio
         Position insertionPos(start.deepEquivalent().upstream());
         // Also avoid the containing list item.
         Node* listChild = enclosingListChild(insertionPos.deprecatedNode());
-        if (listChild && listChild->hasTagName(liTag))
+        if (isHTMLLIElement(listChild))
             insertionPos = positionInParentBeforeNode(*listChild);
 
         insertNodeAt(listElement, insertionPos);