Set the scrollbarLayer as opaque after setupScrollbarLayer.

Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/Source/core/page/scrolling/ScrollingCoordinator.cpp b/Source/core/page/scrolling/ScrollingCoordinator.cpp
index 4784f8db7b5a475a9a5d372440a532d0694c28a1..7b4a9bbecfb7d7b2e52514a3e69be89aa8dec505 100644
--- a/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -334,14 +334,14 @@ void ScrollingCoordinator::scrollableAreaScrollbarLayerDidChange(ScrollableArea*
             scrollbarLayer = addWebScrollbarLayer(scrollableArea, orientation, webScrollbarLayer.release());
         }
 
+        WebLayer* scrollLayer = toWebLayer(scrollableArea->layerForScrolling());
+        WebLayer* containerLayer = toWebLayer(scrollableArea->layerForContainer());
+        setupScrollbarLayer(scrollbarGraphicsLayer, scrollbarLayer, scrollLayer, containerLayer);
+
         // Root layer non-overlay scrollbars should be marked opaque to disable
         // blending.
         bool isOpaqueScrollbar = !scrollbar->isOverlayScrollbar();
         scrollbarGraphicsLayer->setContentsOpaque(isMainFrame && isOpaqueScrollbar);
-
-        WebLayer* scrollLayer = toWebLayer(scrollableArea->layerForScrolling());
-        WebLayer* containerLayer = toWebLayer(scrollableArea->layerForContainer());
-        setupScrollbarLayer(scrollbarGraphicsLayer, scrollbarLayer, scrollLayer, containerLayer);
     } else
         removeWebScrollbarLayer(scrollableArea, orientation);
 }