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

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
index c2ef26e9df87fb2fab748c72d935133908a0bc94..14878b965bced578d4f7f87378289b66d2df1896 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
@@ -59,6 +59,21 @@ ScrollbarThemeOverlay::ScrollbarThemeOverlay(int thumbThickness,
       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;