add Tickmarks to aura overlay scrollbar

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.h b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.h
index 2620014d7c97acfe526c87a2a0528736eb9fad4e..3544ca74ca1c3cfe731915f118f566ca3dfe056f 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.h
@@ -39,6 +39,9 @@ namespace blink {
 class PLATFORM_EXPORT ScrollbarThemeAura : public ScrollbarTheme {
  public:
   int scrollbarThickness(ScrollbarControlSize) override;
+  static void paintAuraTickmarks(GraphicsContext&,

[bokan, 2016/11/04 19:46:25]

Lets just move this implementation into ScrollbarTheme and just override with an
empty implementation in Themes that shouldn't have it. By my count:

-ScrollbarThemeMac overrides with its own impl so that's fine

-ScrollbarThemeMock (and OverlayMock) previously didn't have it but if it
doesn't cause any tests to break it wont hurt to leave it in.

-ScrollbarThemeAndroid didn't have it either but maybe that's ok if it uses its
own implementation through a different path. In any case, we should override
with an empty impl and a comment describing where that happens on Android.

-ScrollbarThemeOverlay and ScrollbarThemeAura can just use the base version we
move into ScrollbarTheme

+                                 const Scrollbar&,
+                                 const IntRect&);
 
  protected:
   bool hasButtons(const ScrollbarThemeClient&) override { return true; }