views: add focus ring to TreeView

ui/views/controls/scroll_view.h

Index: ui/views/controls/scroll_view.h
diff --git a/ui/views/controls/scroll_view.h b/ui/views/controls/scroll_view.h
index 5f55c20d31b7d1bd0aeb883103ae693a73291488..ff444bb8da0d532f60b2f98d48ce5077d38bc120 100644
--- a/ui/views/controls/scroll_view.h
+++ b/ui/views/controls/scroll_view.h
@@ -88,6 +88,9 @@ class VIEWS_EXPORT ScrollView : public View, public ScrollBarController {
   void SetHorizontalScrollBar(ScrollBar* horiz_sb);
   void SetVerticalScrollBar(ScrollBar* vert_sb);
 
+  // Sets whether this ScrollView has a focus ring or not.
+  void SetHasFocusRing(bool has_focus_ring);
+
   // View overrides:
   gfx::Size GetPreferredSize() const override;
   int GetHeightForWidth(int width) const override;
@@ -181,6 +184,9 @@ class VIEWS_EXPORT ScrollView : public View, public ScrollBarController {
   // than the viewport).
   bool hide_horizontal_scrollbar_;
 
+  // Focus ring, if one is installed.
+  View* focus_ring_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(ScrollView);
 };