Revert of Remove indirection: setup scrollbar scroll layers in the scrollbar constructor

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index d50862b8e395b30a3eaa2a3ca9bd325daab42681..367265b73ddcc5698db54cb1171979c80fd23e13 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -3824,6 +3824,12 @@
                                 : nullptr;
 
   VisualViewport& visualViewport = page()->frameHost().visualViewport();
+
+  // TODO(bokan): This was moved here from when registerViewportLayers was a
+  // part of VisualViewport and maybe doesn't belong here. See comment inside
+  // the mehtod.
+  visualViewport.setScrollLayerOnScrollbars(layoutViewportWebLayer);
+
   m_layerTreeView->registerViewportLayers(
       visualViewport.overscrollElasticityLayer()->platformLayer(),
       visualViewport.pageScaleLayer()->platformLayer(),