Replace layer id with Element id for tracking scrollbar animation controllers

cc/layers/solid_color_scrollbar_layer.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_
 #define CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_
 
 #include "base/macros.h"
 #include "cc/cc_export.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/scrollbar_layer_interface.h"
 
 namespace cc {
 
 class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
                                            public Layer {
  public:
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
   static scoped_refptr<SolidColorScrollbarLayer> Create(
       ScrollbarOrientation orientation,
       int thumb_thickness,
       int track_start,
       bool is_left_side_vertical_scrollbar,
-      int scroll_layer_id);
+      int scroll_layer_id,
+      ElementId scroll_element_id);
 
   // Layer overrides.
   bool OpacityCanAnimateOnImplThread() const override;
   bool AlwaysUseActiveTreeOpacity() const override;
   ScrollbarLayerInterface* ToScrollbarLayer() override;
 
   void SetOpacity(float opacity) override;
   void PushPropertiesTo(LayerImpl* layer) override;
 
   void SetNeedsDisplayRect(const gfx::Rect& rect) override;
 
   // ScrollbarLayerInterface
-  int ScrollLayerId() const override;
-  void SetScrollLayer(int layer_id) override;
+  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;
 
   ScrollbarOrientation orientation() const override;
 
   int thumb_thickness() const {
     return solid_color_scrollbar_layer_inputs_.thumb_thickness;
   }
 
   int track_start() const {
     return solid_color_scrollbar_layer_inputs_.track_start;
   }
 
   bool is_left_side_vertical_scrollbar() const {
     return solid_color_scrollbar_layer_inputs_.is_left_side_vertical_scrollbar;
   }
 
  protected:
   SolidColorScrollbarLayer(ScrollbarOrientation orientation,
                            int thumb_thickness,
                            int track_start,
                            bool is_left_side_vertical_scrollbar,
-                           int scroll_layer_id);
+                           int scroll_layer_id,
+                           ElementId scroll_element_id);
   ~SolidColorScrollbarLayer() override;
 
  private:
   friend class LayerSerializationTest;
 
   // Encapsulate all data, callbacks, interfaces received from the embedder.
   struct SolidColorScrollbarLayerInputs {
     SolidColorScrollbarLayerInputs(ScrollbarOrientation orientation,
                                    int thumb_thickness,
                                    int track_start,
                                    bool is_left_side_vertical_scrollbar,
-                                   int scroll_layer_id);
+                                   int scroll_layer_id,
+                                   ElementId scroll_element_id);
     ~SolidColorScrollbarLayerInputs();
 
     int scroll_layer_id;
+    ElementId scroll_element_id;
     ScrollbarOrientation orientation;
     int thumb_thickness;
     int track_start;
     bool is_left_side_vertical_scrollbar;
   };
 
   SolidColorScrollbarLayerInputs solid_color_scrollbar_layer_inputs_;
 
   DISALLOW_COPY_AND_ASSIGN(SolidColorScrollbarLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_