Remove scroll layer ids from scrollbar layers

cc/layers/painted_scrollbar_layer.h

Index: cc/layers/painted_scrollbar_layer.h
diff --git a/cc/layers/painted_scrollbar_layer.h b/cc/layers/painted_scrollbar_layer.h
index 5eacb1ec7e3e96073e67a787f8a4f1eaf0e01f4a..17cf5a6418727cb6848cf3f20bc6ec0c80956afc 100644
--- a/cc/layers/painted_scrollbar_layer.h
+++ b/cc/layers/painted_scrollbar_layer.h
@@ -22,7 +22,6 @@ class CC_EXPORT PaintedScrollbarLayer : public ScrollbarLayerInterface,
 
   static scoped_refptr<PaintedScrollbarLayer> Create(
       std::unique_ptr<Scrollbar> scrollbar,
-      int scroll_layer_id,
       ElementId element_id = ElementId());
 
   bool OpacityCanAnimateOnImplThread() const override;
@@ -31,8 +30,7 @@ class CC_EXPORT PaintedScrollbarLayer : public ScrollbarLayerInterface,
 
   // ScrollbarLayerInterface
   ElementId scroll_element_id() const override;
-  // TODO(pdr): Remove layer_id and refactor scrollbars to just use element ids.
-  void SetScrollInfo(int layer_id, ElementId element_id) override;
+  void SetScrollElementId(ElementId element_id) override;
 
   ScrollbarOrientation orientation() const override;
 
@@ -47,7 +45,6 @@ class CC_EXPORT PaintedScrollbarLayer : public ScrollbarLayerInterface,
 
  protected:
   PaintedScrollbarLayer(std::unique_ptr<Scrollbar> scrollbar,
-                        int scroll_layer_id,
                         ElementId scroll_element_id);
   ~PaintedScrollbarLayer() override;
 
@@ -79,7 +76,6 @@ class CC_EXPORT PaintedScrollbarLayer : public ScrollbarLayerInterface,
                                           ScrollbarPart part);
 
   std::unique_ptr<Scrollbar> scrollbar_;
-  int scroll_layer_id_;
   ElementId scroll_element_id_;
 
   float internal_contents_scale_;