Refactor scroll chaining to use ScrollNodes without going through LayerImpl

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 5fff96cb82cd740d73cfb6dfc542a6d9703d8ce7..1a39e1b57d00e7f47f15a5a20cf3855f68008835 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -59,7 +59,6 @@ class RenderPass;
 class ScrollbarLayerImplBase;
 class SimpleEnclosedRegion;
 class Tile;
-class ScrollState;
 
 struct AppendQuadsData;
 
@@ -90,8 +89,6 @@ class CC_EXPORT LayerImpl {
                             const PropertyAnimationState& state);
   bool IsActive() const;
 
-  void DistributeScroll(ScrollState* scroll_state);
-
   void set_property_tree_sequence_number(int sequence_number) {}
 
   void SetTransformTreeIndex(int index);