Implement overlay scrollbar fade out for non-composited scrollers.

third_party/WebKit/Source/platform/exported/WebScrollbarThemeClientImpl.cpp

 /*
  * Copyright (C) 2012 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 150 matching lines @@
 }
 
 ScrollbarPart WebScrollbarThemeClientImpl::hoveredPart() const {
   return static_cast<ScrollbarPart>(m_scrollbar.hoveredPart());
 }
 
 void WebScrollbarThemeClientImpl::styleChanged() {
   ASSERT_NOT_REACHED();
 }
 
-void WebScrollbarThemeClientImpl::visibilityChanged() {}
+void WebScrollbarThemeClientImpl::setScrollbarsHidden(bool hidden) {
+  ASSERT_NOT_REACHED();
+}
 
 bool WebScrollbarThemeClientImpl::enabled() const {
   return m_scrollbar.enabled();
 }
 
 void WebScrollbarThemeClientImpl::setEnabled(bool) {
   ASSERT_NOT_REACHED();
 }
 
 bool WebScrollbarThemeClientImpl::isOverlayScrollbar() const {
   return m_scrollbar.isOverlay();
 }
 
 float WebScrollbarThemeClientImpl::elasticOverscroll() const {
   return m_scrollbar.elasticOverscroll();
 }
 
 void WebScrollbarThemeClientImpl::setElasticOverscroll(
     float elasticOverscroll) {
   return m_scrollbar.setElasticOverscroll(elasticOverscroll);
 }
 
 }  // namespace blink