GSB uses delta_hints to calculate scrolling chain.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index b8553cb323b236fa95fc6b52fd866c976b5e94a9..bd4dbcc59277f1e411611d2783d686ed73eee293 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -166,7 +166,7 @@ class CC_EXPORT LayerTreeHostImpl
   InputHandler::ScrollStatus RootScrollBegin(
       ScrollState* scroll_state,
       InputHandler::ScrollInputType type) override;
-  ScrollStatus ScrollAnimatedBegin(const gfx::Point& viewport_point) override;
+  ScrollStatus ScrollAnimatedBegin(ScrollState* scroll_state) override;
   InputHandler::ScrollStatus ScrollAnimated(
       const gfx::Point& viewport_point,
       const gfx::Vector2dF& scroll_delta,
@@ -664,6 +664,8 @@ class CC_EXPORT LayerTreeHostImpl
       InputHandler::ScrollInputType type);
   bool IsInitialScrollHitTestReliable(LayerImpl* layer, const gfx::PointF&);
   void DistributeScrollDelta(ScrollState* scroll_state);
+  bool CanConsumeDelta(ScrollNode* scroll_node,
+                       const ScrollState& scroll_state);
 
   bool AnimatePageScale(base::TimeTicks monotonic_time);
   bool AnimateScrollbars(base::TimeTicks monotonic_time);