Add custom action support

ui/accessibility/ax_tree.h

Index: ui/accessibility/ax_tree.h
diff --git a/ui/accessibility/ax_tree.h b/ui/accessibility/ax_tree.h
index 53cd9ea7baeda471161e5d92ccae6908eff9061d..1b01136d3493b323f6961904db47ff201b32e162 100644
--- a/ui/accessibility/ax_tree.h
+++ b/ui/accessibility/ax_tree.h
@@ -83,6 +83,12 @@ class AX_EXPORT AXTreeDelegate {
       AXIntListAttribute attr,
       const std::vector<int32_t>& old_value,
       const std::vector<int32_t>& new_value) {}
+  virtual void OnStringListAttributeChanged(
+      AXTree* tree,
+      AXNode* node,
+      AXStringListAttribute attr,
+      const std::vector<std::string>& old_value,
+      const std::vector<std::string>& new_value) {}
 
   // Called when tree data changes.
   virtual void OnTreeDataChanged(AXTree* tree) = 0;