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

cc/layers/solid_color_scrollbar_layer.cc

Index: cc/layers/solid_color_scrollbar_layer.cc
diff --git a/cc/layers/solid_color_scrollbar_layer.cc b/cc/layers/solid_color_scrollbar_layer.cc
index d67c5e35e7f744f0487caf709ed721bda9641e81..2eb5484c855035419083a89ce65e147cff1a62f2 100644
--- a/cc/layers/solid_color_scrollbar_layer.cc
+++ b/cc/layers/solid_color_scrollbar_layer.cc
@@ -99,6 +99,14 @@
   return solid_color_scrollbar_layer_inputs_.scroll_layer_id;
 }
 
+void SolidColorScrollbarLayer::SetScrollLayer(int layer_id) {
+  if (layer_id == solid_color_scrollbar_layer_inputs_.scroll_layer_id)
+    return;
+
+  solid_color_scrollbar_layer_inputs_.scroll_layer_id = layer_id;
+  SetNeedsFullTreeSync();
+}
+
 ScrollbarOrientation SolidColorScrollbarLayer::orientation() const {
   return solid_color_scrollbar_layer_inputs_.orientation;
 }