Replace layer id with Element id for tracking scrollbar animation controllers

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 2eb5484c855035419083a89ce65e147cff1a62f2..e53941e64a636e6da425eb17f1c3177439bab784 100644
--- a/cc/layers/solid_color_scrollbar_layer.cc
+++ b/cc/layers/solid_color_scrollbar_layer.cc
@@ -27,10 +27,11 @@ scoped_refptr<SolidColorScrollbarLayer> SolidColorScrollbarLayer::Create(
     int thumb_thickness,
     int track_start,
     bool is_left_side_vertical_scrollbar,
-    int scroll_layer_id) {
+    int scroll_layer_id,
+    ElementId scroll_element_id) {
   return make_scoped_refptr(new SolidColorScrollbarLayer(
       orientation, thumb_thickness, track_start,
-      is_left_side_vertical_scrollbar, scroll_layer_id));
+      is_left_side_vertical_scrollbar, scroll_layer_id, scroll_element_id));
 }
 
 SolidColorScrollbarLayer::SolidColorScrollbarLayerInputs::
@@ -38,8 +39,10 @@ SolidColorScrollbarLayer::SolidColorScrollbarLayerInputs::
                                    int thumb_thickness,
                                    int track_start,
                                    bool is_left_side_vertical_scrollbar,
-                                   int scroll_layer_id)
+                                   int scroll_layer_id,
+                                   ElementId scroll_element_id)
     : scroll_layer_id(scroll_layer_id),
+      scroll_element_id(scroll_element_id),
       orientation(orientation),
       thumb_thickness(thumb_thickness),
       track_start(track_start),
@@ -53,12 +56,14 @@ SolidColorScrollbarLayer::SolidColorScrollbarLayer(
     int thumb_thickness,
     int track_start,
     bool is_left_side_vertical_scrollbar,
-    int scroll_layer_id)
+    int scroll_layer_id,
+    ElementId scroll_element_id)
     : solid_color_scrollbar_layer_inputs_(orientation,
                                           thumb_thickness,
                                           track_start,
                                           is_left_side_vertical_scrollbar,
-                                          scroll_layer_id) {
+                                          scroll_layer_id,
+                                          scroll_element_id) {
   Layer::SetOpacity(0.f);
 }
 
@@ -79,8 +84,9 @@ void SolidColorScrollbarLayer::PushPropertiesTo(LayerImpl* layer) {
   SolidColorScrollbarLayerImpl* scrollbar_layer =
       static_cast<SolidColorScrollbarLayerImpl*>(layer);
 
-  scrollbar_layer->SetScrollLayerId(
-      solid_color_scrollbar_layer_inputs_.scroll_layer_id);
+  scrollbar_layer->SetScrollInfo(
+      solid_color_scrollbar_layer_inputs_.scroll_layer_id,
+      solid_color_scrollbar_layer_inputs_.scroll_element_id);
 }
 
 void SolidColorScrollbarLayer::SetNeedsDisplayRect(const gfx::Rect& rect) {
@@ -95,15 +101,18 @@ bool SolidColorScrollbarLayer::AlwaysUseActiveTreeOpacity() const {
   return true;
 }
 
-int SolidColorScrollbarLayer::ScrollLayerId() const {
-  return solid_color_scrollbar_layer_inputs_.scroll_layer_id;
+ElementId SolidColorScrollbarLayer::scroll_element_id() const {
+  return solid_color_scrollbar_layer_inputs_.scroll_element_id;
 }
 
-void SolidColorScrollbarLayer::SetScrollLayer(int layer_id) {
-  if (layer_id == solid_color_scrollbar_layer_inputs_.scroll_layer_id)
+void SolidColorScrollbarLayer::SetScrollInfo(int layer_id,
+                                             ElementId element_id) {
+  if (layer_id == solid_color_scrollbar_layer_inputs_.scroll_layer_id &&
+      element_id == solid_color_scrollbar_layer_inputs_.scroll_element_id)
     return;
 
   solid_color_scrollbar_layer_inputs_.scroll_layer_id = layer_id;
+  solid_color_scrollbar_layer_inputs_.scroll_element_id = element_id;
   SetNeedsFullTreeSync();
 }