Aura Overlay Scrollbars appear when mouse hovers over scroller edge

cc/layers/scrollbar_layer_impl_base.h

Index: cc/layers/scrollbar_layer_impl_base.h
diff --git a/cc/layers/scrollbar_layer_impl_base.h b/cc/layers/scrollbar_layer_impl_base.h
index 5256e631eab4b2ebc55ff2c411b52b8b504af332..7ec930a24d4dcf929d16ff17e8b04f07161bb0cd 100644
--- a/cc/layers/scrollbar_layer_impl_base.h
+++ b/cc/layers/scrollbar_layer_impl_base.h
@@ -54,6 +54,8 @@ class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
   }
   bool SetThumbThicknessScaleFactor(float thumb_thickness_scale_factor);
 
+  virtual int ThumbThickness() const = 0;
+
  protected:
   ScrollbarLayerImplBase(LayerTreeImpl* tree_impl,
                          int id,
@@ -62,7 +64,6 @@ class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
                          bool is_overlay);
   ~ScrollbarLayerImplBase() override;
 
-  virtual int ThumbThickness() const = 0;
   virtual int ThumbLength() const = 0;
   virtual float TrackLength() const = 0;
   virtual int TrackStart() const = 0;