add Tickmarks to aura overlay scrollbar

third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h

Index: third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
index 1d7840e92cd57ac82fa438c6a7e81b007da56c24..86eec510281cc39bc1b4747f0a84ab7d84f9e8f9 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.h
@@ -88,7 +88,7 @@ class PLATFORM_EXPORT ScrollbarTheme {
                                  const IntRect& cornerRect);
   virtual void paintTickmarks(GraphicsContext&,
                               const Scrollbar&,
-                              const IntRect&) {}
+                              const IntRect&);
 
   virtual bool shouldCenterOnThumb(const ScrollbarThemeClient&,
                                    const PlatformMouseEvent&);
@@ -176,6 +176,7 @@ class PLATFORM_EXPORT ScrollbarTheme {
   static bool mockScrollbarsEnabled();
 
  protected:
+  virtual int tickmarkBorderWidth() { return 0; }
   static DisplayItem::Type buttonPartToDisplayItemType(ScrollbarPart);
   static DisplayItem::Type trackPiecePartToDisplayItemType(ScrollbarPart);