Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

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

 /*
  * Copyright (C) 2009, 2010, 2011 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 1918 matching lines @@
     if (m_layerForHorizontalScrollbar && needsHorizontalScrollbarLayer &&
         scrollableArea->shouldRebuildHorizontalScrollbarLayer())
       toggleScrollbarLayerIfNeeded(
           m_layerForHorizontalScrollbar, false,
           CompositingReasonLayerForHorizontalScrollbar);
     if (m_layerForVerticalScrollbar && needsVerticalScrollbarLayer &&
         scrollableArea->shouldRebuildVerticalScrollbarLayer())
       toggleScrollbarLayerIfNeeded(m_layerForVerticalScrollbar, false,
                                    CompositingReasonLayerForVerticalScrollbar);
     scrollableArea->resetRebuildScrollbarLayerFlags();
+
+    if (m_scrollingContentsLayer &&
+        scrollableArea->needsShowScrollbarLayers()) {
+      m_scrollingContentsLayer->platformLayer()->showScrollbars();
+      scrollableArea->didShowScrollbarLayers();
+    }
   }
 
   // If the subtree is invisible, we don't actually need scrollbar layers.
   // Only do this check if at least one of the bits is currently true.
   // This is important because this method is called during the destructor
   // of CompositedLayerMapping, which may happen during style recalc,
   // and therefore visible content status may be invalid.
   if (needsHorizontalScrollbarLayer || needsVerticalScrollbarLayer ||
       needsScrollCornerLayer) {
     bool invisible = m_owningLayer.subtreeIsInvisible();
@@ skipping 1593 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink