GSB uses delta_hints to calculate scrolling chain.

content/browser/renderer_host/input/synthetic_smooth_move_gesture.h

 // Copyright 2013 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 CONTENT_BROWSER_RENDERER_HOST_INPUT_SYNTHETIC_SMOOTH_MOVE_GESTURE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_SYNTHETIC_SMOOTH_MOVE_GESTURE_H_
 
 #include <vector>
 
 #include "base/macros.h"
@@ skipping 56 matching lines @@
 
   void ForwardTouchInputEvents(
       const base::TimeTicks& timestamp, SyntheticGestureTarget* target);
   void ForwardMouseWheelInputEvents(
       const base::TimeTicks& timestamp, SyntheticGestureTarget* target);
   void ForwardMouseClickInputEvents(
       const base::TimeTicks& timestamp, SyntheticGestureTarget* target);
 
   void ForwardMouseWheelEvent(SyntheticGestureTarget* target,
                               const gfx::Vector2dF& delta,
+                              const blink::WebMouseWheelEvent::Phase phase,
                               const base::TimeTicks& timestamp) const;
 
   void PressPoint(SyntheticGestureTarget* target,
                   const base::TimeTicks& timestamp);
   void MovePoint(SyntheticGestureTarget* target,
                  const gfx::Vector2dF& delta,
                  const base::TimeTicks& timestamp);
   void ReleasePoint(SyntheticGestureTarget* target,
                     const base::TimeTicks& timestamp);
 
@@ skipping 15 matching lines @@
   int current_move_segment_;
   base::TimeTicks current_move_segment_start_time_;
   base::TimeTicks current_move_segment_stop_time_;
 
   DISALLOW_COPY_AND_ASSIGN(SyntheticSmoothMoveGesture);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_SYNTHETIC_SMOOTH_MOVE_GESTURE_H_