GSB uses delta_hints to calculate scrolling chain.

third_party/WebKit/Source/core/input/ScrollManager.h

 // Copyright 2016 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 ScrollManager_h
 #define ScrollManager_h
 
 #include <deque>
 #include "core/CoreExport.h"
 #include "core/page/EventWithHitTestResults.h"
@@ skipping 82 matching lines @@
 
  private:
   WebInputEventResult HandleGestureScrollUpdate(const WebGestureEvent&);
   WebInputEventResult HandleGestureScrollBegin(const WebGestureEvent&);
 
   WebInputEventResult PassScrollGestureEvent(const WebGestureEvent&,
                                              LayoutObject*);
 
   void ClearGestureScrollState();
 
-  void CustomizedScroll(const Node& start_node, ScrollState&);
+  void CustomizedScroll(ScrollState&);
 
   Page* GetPage() const;
 
   bool IsViewportScrollingElement(const Element&) const;
 
   bool HandleScrollGestureOnResizer(Node*, const WebGestureEvent&);
 
   void RecomputeScrollChain(const Node& start_node,
+                            const ScrollState&,
                             std::deque<int>& scroll_chain);
+  bool CanScroll(const ScrollState&, const Element* current_element);
 
   // scroller_size is set only when scrolling non root scroller.
   void ComputeScrollRelatedMetrics(
       uint32_t* non_composited_main_thread_scrolling_reasons,
       int* scroller_size);
   void RecordScrollRelatedMetrics(const WebGestureDevice);
 
   // NOTE: If adding a new field to this class please ensure that it is
   // cleared in |ScrollManager::clear()|.
 
@@ skipping 23 matching lines @@
 
   Member<PaintLayerScrollableArea> resize_scrollable_area_;
 
   LayoutSize
       offset_from_resize_corner_;  // In the coords of m_resizeScrollableArea.
 };
 
 }  // namespace blink
 
 #endif  // ScrollManager_h