Arrange compositor scrolling into scroll customization format

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 27bf2ac156b59caa497f36a086f3a130a6344395..23d6df7f46314fd8805257b88d97919b8dd1ee31 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -67,6 +67,7 @@ class ScrollbarLayerImplBase;
 class SimpleEnclosedRegion;
 class Tile;
 class TransformTree;
+class ScrollState;
 
 struct AppendQuadsData;
 
@@ -149,6 +150,9 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
     return scroll_children_.get();
   }
 
+  void DistributeScroll(ScrollState* scroll_state);
+  void ApplyScroll(ScrollState* scroll_state);
+
   void set_property_tree_sequence_number(int sequence_number) {}
 
   void SetTransformTreeIndex(int index);