Remove scroll layer ids from scrollbar layers

cc/layers/solid_color_scrollbar_layer.h

Index: cc/layers/solid_color_scrollbar_layer.h
diff --git a/cc/layers/solid_color_scrollbar_layer.h b/cc/layers/solid_color_scrollbar_layer.h
index 814851c9333d2ae078ff8f1a4673b50803b091c6..93b819c1bf9001ca410c45ce9317edd03a855dc3 100644
--- a/cc/layers/solid_color_scrollbar_layer.h
+++ b/cc/layers/solid_color_scrollbar_layer.h
@@ -22,7 +22,6 @@ class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
       int thumb_thickness,
       int track_start,
       bool is_left_side_vertical_scrollbar,
-      int scroll_layer_id,
       ElementId scroll_element_id);
 
   // Layer overrides.
@@ -37,8 +36,7 @@ class CC_EXPORT SolidColorScrollbarLayer : 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;
 
@@ -59,7 +57,6 @@ class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
                            int thumb_thickness,
                            int track_start,
                            bool is_left_side_vertical_scrollbar,
-                           int scroll_layer_id,
                            ElementId scroll_element_id);
   ~SolidColorScrollbarLayer() override;
 
@@ -72,11 +69,9 @@ class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
                                    int thumb_thickness,
                                    int track_start,
                                    bool is_left_side_vertical_scrollbar,
-                                   int scroll_layer_id,
                                    ElementId scroll_element_id);
     ~SolidColorScrollbarLayerInputs();
 
-    int scroll_layer_id;
     ElementId scroll_element_id;
     ScrollbarOrientation orientation;
     int thumb_thickness;