views: add focus ring to TreeView

ui/views/controls/focus_ring.h

Index: ui/views/controls/focus_ring.h
diff --git a/ui/views/controls/focus_ring.h b/ui/views/controls/focus_ring.h
index 2438bc7b9dd5f215359deddab148669cc2f798a6..d0f2703094885590c89fb7b9e435e8c3a4e7edde 100644
--- a/ui/views/controls/focus_ring.h
+++ b/ui/views/controls/focus_ring.h
@@ -14,6 +14,8 @@ namespace views {
 // the bounds of its parent view.
 class FocusRing : public View {
  public:
+  static const char kViewClassName[];
+
   // Create a FocusRing and adds it to |parent|.
   static void Install(views::View* parent);
 
@@ -27,8 +29,6 @@ class FocusRing : public View {
   void OnPaint(gfx::Canvas* canvas) override;
 
  private:
-  static const char kViewClassName[];
-
   FocusRing();
   ~FocusRing() override;