Re-target wheel events only when a new scroll sequence has started.

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

Index: third_party/WebKit/Source/core/input/MouseWheelEventManager.h
diff --git a/third_party/WebKit/Source/core/input/MouseWheelEventManager.h b/third_party/WebKit/Source/core/input/MouseWheelEventManager.h
index ecf2e5ae20750706cc8dcc845e5441787b4fdc28..809ed02c4672b104f322bc59faa8989b0b689a6a 100644
--- a/third_party/WebKit/Source/core/input/MouseWheelEventManager.h
+++ b/third_party/WebKit/Source/core/input/MouseWheelEventManager.h
@@ -11,7 +11,10 @@
 
 namespace blink {
 
+class Document;
 class LocalFrame;
+class LocalFrameView;
+class Node;
 class ScrollManager;
 class WebMouseWheelEvent;
 
@@ -23,10 +26,17 @@ class MouseWheelEventManager final
   explicit MouseWheelEventManager(LocalFrame&, ScrollManager&);
   DECLARE_TRACE();
 
+  void Clear();
+
   WebInputEventResult HandleWheelEvent(const WebMouseWheelEvent&);
 
  private:
+  Node* FindTargetNode(const WebMouseWheelEvent&,
+                       const Document*,
+                       const LocalFrameView*);
+
   const Member<LocalFrame> frame_;
+  Member<Node> wheel_target_;
   Member<ScrollManager> scroll_manager_;
 };