Add Traversal<*Element>::firstAncestor() API

Source/core/accessibility/AXNodeObject.cpp

Index: Source/core/accessibility/AXNodeObject.cpp
diff --git a/Source/core/accessibility/AXNodeObject.cpp b/Source/core/accessibility/AXNodeObject.cpp
index 76381e162810bd626d81db51b243b4e1d33209e3..f7d4c591bb43089dbfe32702dd8dc14bb73edfd0 100644
--- a/Source/core/accessibility/AXNodeObject.cpp
+++ b/Source/core/accessibility/AXNodeObject.cpp
@@ -1467,13 +1467,10 @@ HTMLLabelElement* AXNodeObject::labelElementContainer() const
     if (isControl())
         return 0;
 
-    // find if this has a parent that is a label
-    for (Node* parentNode = node(); parentNode; parentNode = parentNode->parentNode()) {
-        if (isHTMLLabelElement(*parentNode))
-            return toHTMLLabelElement(parentNode);
-    }
-
-    return 0;
+    // find if this has a ancestor that is a label
+    if (isHTMLLabelElement(*node()))
+        return toHTMLLabelElement(node());
+    return Traversal<HTMLLabelElement>::firstAncestor(*node());
 }
 
 void AXNodeObject::setFocused(bool on)