Feed ScrollableArea::showOverlayScrollbars into ScrollbarAnimationController.

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index ffe33d94e50aa39bb66a4789bd403afe6cb2c93c..0223e111eef964798c44faa9140f787eb2fc5057 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -1926,6 +1926,12 @@ bool CompositedLayerMapping::updateOverflowControlsLayers(
       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.