Enables hot-tracking for overflow extension buttons in the app menu

ui/native_theme/native_theme.h

Index: ui/native_theme/native_theme.h
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index b09dd15b1c17171fe6dffbb7aa1f9b100bd4e920..f4dbd690a7edffe0645b6a3bca0472f367c749dd 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -132,6 +132,7 @@ class NATIVE_THEME_EXPORT NativeTheme {
 
   struct MenuItemExtraParams {
     bool is_selected;
+    int corner_radius;
   };
 
   struct MenuListExtraParams {
@@ -196,7 +197,9 @@ class NATIVE_THEME_EXPORT NativeTheme {
     int classic_state;  // Used on Windows when uxtheme is not available.
   };
 
-  union ExtraParams {
+  union NATIVE_THEME_EXPORT ExtraParams {
+    ExtraParams();
+
     ButtonExtraParams button;
     InnerSpinButtonExtraParams inner_spin;
     MenuArrowExtraParams menu_arrow;