Remove scroll layer ids from scrollbar layers

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 2aa29c4ff113d47a7b804cac09b11cdbc14408b7..5ab2eaed4b938f14d273942e007ea15fb70e6885 100644
--- a/cc/layers/painted_overlay_scrollbar_layer.cc
+++ b/cc/layers/painted_overlay_scrollbar_layer.cc
@@ -32,18 +32,15 @@ std::unique_ptr<LayerImpl> PaintedOverlayScrollbarLayer::CreateLayerImpl(
 
 scoped_refptr<PaintedOverlayScrollbarLayer>
 PaintedOverlayScrollbarLayer::Create(std::unique_ptr<Scrollbar> scrollbar,
-                                     int scroll_layer_id,
                                      ElementId scroll_element_id) {
   return make_scoped_refptr(new PaintedOverlayScrollbarLayer(
-      std::move(scrollbar), scroll_layer_id, scroll_element_id));
+      std::move(scrollbar), scroll_element_id));
 }
 
 PaintedOverlayScrollbarLayer::PaintedOverlayScrollbarLayer(
     std::unique_ptr<Scrollbar> scrollbar,
-    int scroll_layer_id,
     ElementId scroll_element_id)
     : scrollbar_(std::move(scrollbar)),
-      scroll_layer_id_(scroll_layer_id),
       scroll_element_id_(scroll_element_id),
       thumb_thickness_(scrollbar_->ThumbThickness()),
       thumb_length_(scrollbar_->ThumbLength()) {
@@ -56,12 +53,10 @@ ElementId PaintedOverlayScrollbarLayer::scroll_element_id() const {
   return scroll_element_id_;
 }
 
-void PaintedOverlayScrollbarLayer::SetScrollInfo(int layer_id,
-                                                 ElementId element_id) {
-  if (layer_id == scroll_layer_id_ && element_id == scroll_element_id_)
+void PaintedOverlayScrollbarLayer::SetScrollElementId(ElementId element_id) {
+  if (element_id == scroll_element_id_)
     return;
 
-  scroll_layer_id_ = layer_id;
   scroll_element_id_ = element_id;
   SetNeedsFullTreeSync();
 }
@@ -84,7 +79,7 @@ void PaintedOverlayScrollbarLayer::PushPropertiesTo(LayerImpl* layer) {
   PaintedOverlayScrollbarLayerImpl* scrollbar_layer =
       static_cast<PaintedOverlayScrollbarLayerImpl*>(layer);
 
-  scrollbar_layer->SetScrollInfo(scroll_layer_id_, scroll_element_id_);
+  scrollbar_layer->SetScrollElementId(scroll_element_id_);
 
   scrollbar_layer->SetThumbThickness(thumb_thickness_);
   scrollbar_layer->SetThumbLength(thumb_length_);