views: add focus ring to TreeView

ui/views/controls/focus_ring.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_CONTROLS_FOCUS_RING_H_
 #define UI_VIEWS_CONTROLS_FOCUS_RING_H_
 
 #include "ui/views/view.h"
 
 namespace views {
 
 // FocusRing is a View that is designed to act as an indicator of focus for its
 // parent. It is a stand-alone view that paints to a layer which extends beyond
 // 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);
 
   // Removes the FocusRing from |parent|.
   static void Uninstall(views::View* parent);
 
   // View:
   const char* GetClassName() const override;
   bool CanProcessEventsWithinSubtree() const override;
   void Layout() override;
   void OnPaint(gfx::Canvas* canvas) override;
 
  private:
-  static const char kViewClassName[];
-
   FocusRing();
   ~FocusRing() override;
 
   DISALLOW_COPY_AND_ASSIGN(FocusRing);
 };
 
 }  // views
 
 #endif  // UI_VIEWS_CONTROLS_FOCUS_RING_H_