Remove indirection: setup scrollbar scroll layers in the scrollbar constructor

cc/layers/painted_overlay_scrollbar_layer.cc

Index: cc/layers/painted_overlay_scrollbar_layer.cc
diff --git a/cc/layers/painted_overlay_scrollbar_layer.cc b/cc/layers/painted_overlay_scrollbar_layer.cc
index ab8643ecac019f803376b6168a43c2dd7a04778a..4f64e9e3d7dce2176ff0bfe13351fab150df6373 100644
--- a/cc/layers/painted_overlay_scrollbar_layer.cc
+++ b/cc/layers/painted_overlay_scrollbar_layer.cc
@@ -52,14 +52,6 @@ int PaintedOverlayScrollbarLayer::ScrollLayerId() const {
   return scroll_layer_id_;
 }
 
-void PaintedOverlayScrollbarLayer::SetScrollLayer(int layer_id) {
-  if (layer_id == scroll_layer_id_)
-    return;
-
-  scroll_layer_id_ = layer_id;
-  SetNeedsFullTreeSync();
-}
-
 bool PaintedOverlayScrollbarLayer::OpacityCanAnimateOnImplThread() const {
   return scrollbar_->IsOverlay();
 }