Add AX role ,'AXDescriptionList', for dl element(re-land).

Source/core/accessibility/AXList.cpp

Index: Source/core/accessibility/AXList.cpp
diff --git a/Source/core/accessibility/AXList.cpp b/Source/core/accessibility/AXList.cpp
index 2f316edcd31842645a700befe7c4a33174798ffc..042c0c5ea511eb0753f766bc8dbbc54116582837 100644
--- a/Source/core/accessibility/AXList.cpp
+++ b/Source/core/accessibility/AXList.cpp
@@ -56,4 +56,20 @@ bool AXList::computeAccessibilityIsIgnored() const
     return accessibilityIsIgnoredByDefault();
 }
 
+bool AXList::isDescriptionList() const
+{
+    if (!m_renderer)
+        return false;
+
+    Node* node = m_renderer->node();
+    return node && node->hasTagName(dlTag);
+}
+
+AccessibilityRole AXList::roleValue() const
+{
+    if (isDescriptionList())
+        return DescriptionListRole;
+
+    return ListRole;
+}
 } // namespace blink