select.add() should support optgroup adding and before index

Source/core/html/HTMLSelectElement.cpp

Index: Source/core/html/HTMLSelectElement.cpp
diff --git a/Source/core/html/HTMLSelectElement.cpp b/Source/core/html/HTMLSelectElement.cpp
index eaed769fd7c3b461c72fbcee405535bbd3b1f196..e05c7b801d98ad5e4418231d62e48c989be29774 100644
--- a/Source/core/html/HTMLSelectElement.cpp
+++ b/Source/core/html/HTMLSelectElement.cpp
@@ -203,13 +203,19 @@ void HTMLSelectElement::add(HTMLElement* element, HTMLElement* before, Exception
     // Make sure the element is ref'd and deref'd so we don't leak it.
     RefPtr<HTMLElement> protectNewChild(element);
 
-    if (!element || !(isHTMLOptionElement(element) || isHTMLHRElement(element)))
+    if (!element || !(isHTMLOptionElement(element) || isHTMLOptGroupElement(element) || isHTMLHRElement(element)))
         return;
 
     insertBefore(element, before, exceptionState);
     setNeedsValidityCheck();
 }
 
+void HTMLSelectElement::addBeforeOptionAtIndex(HTMLElement* element, unsigned beforeIndex, ExceptionState& exceptionState)
+{
+    HTMLElement* beforeElement = toHTMLElement(options()->item(beforeIndex));
+    add(element, beforeElement, exceptionState);
+}
+
 void HTMLSelectElement::remove(int optionIndex)
 {
     int listIndex = optionToListIndex(optionIndex);