Track the currently scrolling ScrollNode instead of the scrolling layer

cc/trees/layer_tree_impl.h

 // Copyright 2012 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_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 158 matching lines @@
   }
 
   LayerImpl* InnerViewportScrollLayer() const;
   // This function may return NULL, it is the caller's responsibility to check.
   LayerImpl* OuterViewportScrollLayer() const;
   gfx::ScrollOffset TotalScrollOffset() const;
   gfx::ScrollOffset TotalMaxScrollOffset() const;
 
   LayerImpl* InnerViewportContainerLayer() const;
   LayerImpl* OuterViewportContainerLayer() const;
-  LayerImpl* CurrentlyScrollingLayer() const;
-  int LastScrolledLayerId() const;
-  void SetCurrentlyScrollingLayer(LayerImpl* layer);
-  void ClearCurrentlyScrollingLayer();
+  ScrollNode* CurrentlyScrollingNode();
+  const ScrollNode* CurrentlyScrollingNode() const;
+  int LastScrolledScrollNodeIndex() const;
+  void SetCurrentlyScrollingNode(ScrollNode* node);
+  void ClearCurrentlyScrollingNode();
 
   void SetViewportLayersFromIds(int overscroll_elasticity_layer,
                                 int page_scale_layer_id,
                                 int inner_viewport_scroll_layer_id,
                                 int outer_viewport_scroll_layer_id);
   void ClearViewportLayers();
   LayerImpl* OverscrollElasticityLayer() {
     return LayerById(overscroll_elasticity_layer_id_);
   }
   LayerImpl* PageScaleLayer() { return LayerById(page_scale_layer_id_); }
@@ skipping 278 matching lines @@
 
   LayerTreeHostImpl* layer_tree_host_impl_;
   int source_frame_number_;
   int is_first_frame_after_commit_tracker_;
   LayerImpl* root_layer_for_testing_;
   HeadsUpDisplayLayerImpl* hud_layer_;
   PropertyTrees property_trees_;
   SkColor background_color_;
   bool has_transparent_background_;
 
-  int last_scrolled_layer_id_;
+  int last_scrolled_scroll_node_index_;
   int overscroll_elasticity_layer_id_;
   int page_scale_layer_id_;
   int inner_viewport_scroll_layer_id_;
   int outer_viewport_scroll_layer_id_;
 
   LayerSelection selection_;
 
   scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor_;
   float min_page_scale_factor_;
   float max_page_scale_factor_;
@@ skipping 70 matching lines @@
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_