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

cc/blink/web_compositor_support_impl.cc

Index: cc/blink/web_compositor_support_impl.cc
diff --git a/cc/blink/web_compositor_support_impl.cc b/cc/blink/web_compositor_support_impl.cc
index 6a5cdf838935bf14298efc91c99f61196eb29f4f..7bb783e571639f56cf8bce033cc2e443cd95b58d 100644
--- a/cc/blink/web_compositor_support_impl.cc
+++ b/cc/blink/web_compositor_support_impl.cc
@@ -65,20 +65,18 @@
 WebCompositorSupportImpl::createScrollbarLayer(
     std::unique_ptr<WebScrollbar> scrollbar,
     WebScrollbarThemePainter painter,
-    std::unique_ptr<WebScrollbarThemeGeometry> geometry,
-    blink::WebLayer* scroll_layer) {
-  return base::MakeUnique<WebScrollbarLayerImpl>(
-      std::move(scrollbar), painter, std::move(geometry), false, scroll_layer);
+    std::unique_ptr<WebScrollbarThemeGeometry> geometry) {
+  return base::MakeUnique<WebScrollbarLayerImpl>(std::move(scrollbar), painter,
+                                                 std::move(geometry));
 }
 
 std::unique_ptr<WebScrollbarLayer>
 WebCompositorSupportImpl::createOverlayScrollbarLayer(
     std::unique_ptr<WebScrollbar> scrollbar,
     WebScrollbarThemePainter painter,
-    std::unique_ptr<WebScrollbarThemeGeometry> geometry,
-    blink::WebLayer* scroll_layer) {
-  return base::MakeUnique<WebScrollbarLayerImpl>(
-      std::move(scrollbar), painter, std::move(geometry), true, scroll_layer);
+    std::unique_ptr<WebScrollbarThemeGeometry> geometry) {
+  return base::MakeUnique<WebScrollbarLayerImpl>(std::move(scrollbar), painter,
+                                                 std::move(geometry), true);
 }
 
 std::unique_ptr<WebScrollbarLayer>
@@ -86,11 +84,10 @@
     WebScrollbar::Orientation orientation,
     int thumb_thickness,
     int track_start,
-    bool is_left_side_vertical_scrollbar,
-    blink::WebLayer* scroll_layer) {
+    bool is_left_side_vertical_scrollbar) {
   return base::MakeUnique<WebScrollbarLayerImpl>(
       orientation, thumb_thickness, track_start,
-      is_left_side_vertical_scrollbar, scroll_layer);
+      is_left_side_vertical_scrollbar);
 }
 
 }  // namespace cc_blink