Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 631 matching lines @@
   }
 
   // Scroll position = scroll origin + scroll offset. Adjust the layer's
   // position to handle whatever the scroll coordinator isn't handling.
   // The scroll origin is non-zero for RTL pages with overflow.
   if (scrollingCoordinatorHandlesOffset)
     m_scrollLayer->setPosition(frameView->scrollOrigin());
   else
     m_scrollLayer->setPosition(IntPoint(-scrollOffset));
 
+  showScrollbarLayersIfNeeded();
+
   DEFINE_STATIC_LOCAL(EnumerationHistogram, acceleratedBackgroundHistogram,
                       ("Renderer.AcceleratedFixedRootBackground",
                        AcceleratedFixedRootBackgroundHistogramMax));
   acceleratedBackgroundHistogram.count(ScrolledMainFrameBucket);
 }
 
 void PaintLayerCompositor::frameViewScrollbarsExistenceDidChange() {
   if (m_containerLayer)
     updateOverflowControlsLayers();
 }
@@ skipping 409 matching lines @@
       m_layerForScrollCorner = GraphicsLayer::create(this);
 
     if (m_layerForScrollCorner->parent() != controlsParent)
       controlsParent->addChild(m_layerForScrollCorner.get());
   } else if (m_layerForScrollCorner) {
     m_layerForScrollCorner->removeFromParent();
     m_layerForScrollCorner = nullptr;
   }
 
   m_layoutView.frameView()->positionScrollbarLayers();
+  showScrollbarLayersIfNeeded();
+}
+
+void PaintLayerCompositor::showScrollbarLayersIfNeeded() {
+  FrameView* frameView = m_layoutView.frameView();
+  if (m_scrollLayer && frameView->needsShowScrollbarLayers()) {
+    m_scrollLayer->platformLayer()->showScrollbars();
+    frameView->didShowScrollbarLayers();
+  }
 }
 
 void PaintLayerCompositor::ensureRootLayer() {
   if (m_rootLayerAttachment != RootLayerUnattached)
     return;
 
   if (isMainFrame())
     visualViewport().createLayerTree();
 
   // When RLS is enabled, none of the PLC GraphicsLayers exist.
@@ skipping 215 matching lines @@
   } else if (graphicsLayer == m_scrollLayer.get()) {
     name = "Frame Scrolling Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink