views: add focus ring to TreeView

ui/views/style/platform_style.h

Index: ui/views/style/platform_style.h
diff --git a/ui/views/style/platform_style.h b/ui/views/style/platform_style.h
index b4cf8deba49e45b235a1634ad8ef74d6903e5c70..411506ca8c381b25fa13d5a3a3e3cce9d64eecb1 100644
--- a/ui/views/style/platform_style.h
+++ b/ui/views/style/platform_style.h
@@ -48,6 +48,9 @@ class VIEWS_EXPORT PlatformStyle {
   // The menu button's action to show the menu.
   static const CustomButton::NotifyAction kMenuNotifyActivationAction;
 
+  // Whether TreeViews get a focus ring on the entire TreeView when focused.
+  static const bool kTreeViewHasFocusRing;
+
   // Whether selecting a row in a TreeView selects the entire row or only the
   // label for that row.
   static const bool kTreeViewSelectionPaintsEntireRow;