Aura overlay scrollbars shouldn't invalidate thumb on scroll or enabled state.

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h
index d746291a522d339095ccd0da569927ea065f8bfd..0772e2136ff5d47dbe0f8151b79f6ecf15aee58b 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.h
@@ -46,6 +46,15 @@ class PLATFORM_EXPORT ScrollbarThemeOverlay : public ScrollbarTheme {
                         Color);
   ~ScrollbarThemeOverlay() override {}
 
+  bool shouldRepaintAllPartsOnInvalidation() const override;
+
+  ScrollbarPart invalidateOnThumbPositionChange(
+      const ScrollbarThemeClient&,
+      float oldPosition,
+      float newPosition) const override;
+
+  ScrollbarPart invalidateOnEnabledChange() const override;
+
   int scrollbarThickness(ScrollbarControlSize) override;
   int scrollbarMargin() const override;
   bool usesOverlayScrollbars() const override;