Remove scroll layer ids from scrollbar layers

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index 5ff22021327e1cae4585b5570a6ccfc66d633649..0f2e083d0f9974cbc0cc7289c8f521fb9ccc39a0 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -34,18 +34,15 @@ std::unique_ptr<LayerImpl> PaintedScrollbarLayer::CreateLayerImpl(
 
 scoped_refptr<PaintedScrollbarLayer> PaintedScrollbarLayer::Create(
     std::unique_ptr<Scrollbar> scrollbar,
-    int scroll_layer_id,
     ElementId scroll_element_id) {
-  return make_scoped_refptr(new PaintedScrollbarLayer(
-      std::move(scrollbar), scroll_layer_id, scroll_element_id));
+  return make_scoped_refptr(
+      new PaintedScrollbarLayer(std::move(scrollbar), scroll_element_id));
 }
 
 PaintedScrollbarLayer::PaintedScrollbarLayer(
     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),
       internal_contents_scale_(1.f),
       thumb_thickness_(scrollbar_->ThumbThickness()),
@@ -64,11 +61,10 @@ ElementId PaintedScrollbarLayer::scroll_element_id() const {
   return scroll_element_id_;
 }
 
-void PaintedScrollbarLayer::SetScrollInfo(int layer_id, ElementId element_id) {
-  if (layer_id == scroll_layer_id_ && element_id == scroll_element_id_)
+void PaintedScrollbarLayer::SetScrollElementId(ElementId element_id) {
+  if (element_id == scroll_element_id_)
     return;
 
-  scroll_layer_id_ = layer_id;
   scroll_element_id_ = element_id;
   SetNeedsFullTreeSync();
 }
@@ -91,7 +87,7 @@ void PaintedScrollbarLayer::PushPropertiesTo(LayerImpl* layer) {
   PaintedScrollbarLayerImpl* scrollbar_layer =
       static_cast<PaintedScrollbarLayerImpl*>(layer);
 
-  scrollbar_layer->SetScrollInfo(scroll_layer_id_, scroll_element_id_);
+  scrollbar_layer->SetScrollElementId(scroll_element_id_);
   scrollbar_layer->set_internal_contents_scale_and_bounds(
       internal_contents_scale_, internal_content_bounds_);