Add handling to respect role attribute in AXObjects.

Source/modules/accessibility/AXListBox.cpp

Index: Source/modules/accessibility/AXListBox.cpp
diff --git a/Source/modules/accessibility/AXListBox.cpp b/Source/modules/accessibility/AXListBox.cpp
index b0410b3cc4e53d8bce90ba2dee635075097eae8c..6048272a83bc53aceeec4e67dd1bf0bf8ee040a9 100644
--- a/Source/modules/accessibility/AXListBox.cpp
+++ b/Source/modules/accessibility/AXListBox.cpp
@@ -51,4 +51,12 @@ PassRefPtr<AXListBox> AXListBox::create(LayoutObject* layoutObject, AXObjectCach
     return adoptRef(new AXListBox(layoutObject, axObjectCache));
 }
 
+AccessibilityRole AXListBox::roleValue() const
+{
+    AccessibilityRole ariaRole = ariaRoleAttribute();
+    if (ariaRole != UnknownRole)
+        return ariaRole;
+    return ListBoxRole;
+}
+
 } // namespace blink