Introduce isHTMLOptGroupElement and toHTMLOptGroupElement

Source/core/rendering/RenderMenuList.cpp

Index: Source/core/rendering/RenderMenuList.cpp
diff --git a/Source/core/rendering/RenderMenuList.cpp b/Source/core/rendering/RenderMenuList.cpp
index 6b3d43f69f0debeb1756fe0e37998898a57d0ffe..547b94c5a847893c434abd4200dad56f50a72f8d 100644
--- a/Source/core/rendering/RenderMenuList.cpp
+++ b/Source/core/rendering/RenderMenuList.cpp
@@ -399,8 +399,8 @@ String RenderMenuList::itemText(unsigned listIndex) const
 
     String itemString;
     Element* element = listItems[listIndex];
-    if (element->hasTagName(optgroupTag))
-        itemString = static_cast<const HTMLOptGroupElement*>(element)->groupLabelText();
+    if (isHTMLOptGroupElement(element))
+        itemString = toHTMLOptGroupElement(element)->groupLabelText();
     else if (element->hasTagName(optionTag))
         itemString = toHTMLOptionElement(element)->textIndentedToRespectGroupLabel();
 
@@ -446,7 +446,7 @@ bool RenderMenuList::itemIsEnabled(unsigned listIndex) const
 
     bool groupEnabled = true;
     if (Element* parentElement = element->parentElement()) {
-        if (parentElement->hasTagName(optgroupTag))
+        if (isHTMLOptGroupElement(parentElement))
             groupEnabled = !parentElement->isDisabledFormControl();
     }
     if (!groupEnabled)
@@ -590,7 +590,7 @@ bool RenderMenuList::itemIsSeparator(unsigned listIndex) const
 bool RenderMenuList::itemIsLabel(unsigned listIndex) const
 {
     const Vector<HTMLElement*>& listItems = selectElement()->listItems();
-    return listIndex < listItems.size() && listItems[listIndex]->hasTagName(optgroupTag);
+    return listIndex < listItems.size() && isHTMLOptGroupElement(listItems[listIndex]);
 }
 
 bool RenderMenuList::itemIsSelected(unsigned listIndex) const