GSB uses delta_hints to calculate scrolling chain.

cc/input/scroll_state.h

 // Copyright 2015 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_INPUT_SCROLL_STATE_H_
 #define CC_INPUT_SCROLL_STATE_H_
 
 #include <list>
 #include <memory>
 
@@ skipping 16 matching lines @@
 
   // Reduce deltas by x, y.
   void ConsumeDelta(double x, double y);
   // Pops the first layer off of |scroll_chain_| and calls
   // |DistributeScroll| on it.
   void DistributeToScrollChainDescendant();
   // Positive when scrolling right.
   double delta_x() const { return data_.delta_x; }
   // Positive when scrolling down.
   double delta_y() const { return data_.delta_y; }
+  // Positive when scrolling right.
+  double delta_x_hint() const { return data_.delta_x_hint; }
+  // Positive when scrolling down.
+  double delta_y_hint() const { return data_.delta_y_hint; }
+  bool ignore_delta_hints() const { return data_.ignore_delta_hints; }
   // The location associated with this scroll update. For touch, this is the
   // position of the finger. For mouse, the location of the cursor.
   int position_x() const { return data_.position_x; }
   int position_y() const { return data_.position_y; }
 
   double velocity_x() const { return data_.velocity_x; }
   double velocity_y() const { return data_.velocity_y; }
 
   bool is_beginning() const { return data_.is_beginning; }
   void set_is_beginning(bool is_beginning) {
@@ skipping 51 matching lines @@
 
  private:
   ScrollStateData data_;
   LayerTreeImpl* layer_tree_impl_;
   std::list<ScrollNode*> scroll_chain_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLL_STATE_H_