Add handling to respect role attribute in AXObjects.

Source/modules/accessibility/AXListBoxOption.cpp

Index: Source/modules/accessibility/AXListBoxOption.cpp
diff --git a/Source/modules/accessibility/AXListBoxOption.cpp b/Source/modules/accessibility/AXListBoxOption.cpp
index 7df76a2fccd69df5c53f812668554de72885fc9f..58a91d3a8961d74c081a87413373c69a193e9678 100644
--- a/Source/modules/accessibility/AXListBoxOption.cpp
+++ b/Source/modules/accessibility/AXListBoxOption.cpp
@@ -53,6 +53,14 @@ PassRefPtr<AXListBoxOption> AXListBoxOption::create(LayoutObject* layoutObject,
     return adoptRef(new AXListBoxOption(layoutObject, axObjectCache));
 }
 
+AccessibilityRole AXListBoxOption::roleValue() const
+{
+    AccessibilityRole ariaRole = ariaRoleAttribute();
+    if (ariaRole != UnknownRole)
+        return ariaRole;
+    return ListBoxOptionRole;
+}
+
 bool AXListBoxOption::isEnabled() const
 {
     if (!node())