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

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

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 41 matching lines @@
 
 ScrollbarThemeOverlay::ScrollbarThemeOverlay(int thumbThickness,
                                              int scrollbarMargin,
                                              HitTestBehavior allowHitTest)
     : ScrollbarTheme(),
       m_thumbThickness(thumbThickness),
       m_scrollbarMargin(scrollbarMargin),
       m_allowHitTest(allowHitTest),
       m_useSolidColor(false) {}
 
+bool ScrollbarThemeOverlay::shouldRepaintAllPartsOnInvalidation() const {
+  return false;
+}
+
+ScrollbarPart ScrollbarThemeOverlay::invalidateOnThumbPositionChange(
+    const ScrollbarThemeClient&,
+    float oldPosition,
+    float newPosition) const {
+  return NoPart;
+}
+
+ScrollbarPart ScrollbarThemeOverlay::invalidateOnEnabledChange() const {
+  return NoPart;
+}
+
 int ScrollbarThemeOverlay::scrollbarThickness(
     ScrollbarControlSize controlSize) {
   return m_thumbThickness + m_scrollbarMargin;
 }
 
 int ScrollbarThemeOverlay::scrollbarMargin() const {
   return m_scrollbarMargin;
 }
 
 bool ScrollbarThemeOverlay::usesOverlayScrollbars() const {
@@ skipping 144 matching lines @@
       Platform::current()->themeEngine()->getOverlayScrollbarStyle(&style);
     }
     theme = new ScrollbarThemeOverlay(
         style.thumbThickness, style.scrollbarMargin,
         ScrollbarThemeOverlay::DisallowHitTest, Color(style.color));
   }
   return *theme;
 }
 
 }  // namespace blink