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..7146f3798b50f840d761f8969ed22ef7533ccdb0 100644
--- a/third_party/WebKit/Source/core/input/MouseWheelEventManager.h
+++ b/third_party/WebKit/Source/core/input/MouseWheelEventManager.h
@@ -12,6 +12,7 @@
 namespace blink {
 
 class LocalFrame;
+class Node;
 class ScrollManager;
 class WebMouseWheelEvent;
 
@@ -23,10 +24,13 @@ class MouseWheelEventManager final
   explicit MouseWheelEventManager(LocalFrame&, ScrollManager&);
   DECLARE_TRACE();
 
+  void Clear();
+
   WebInputEventResult HandleWheelEvent(const WebMouseWheelEvent&);
 
  private:
   const Member<LocalFrame> frame_;
+  Member<Node> wheel_target_;
   Member<ScrollManager> scroll_manager_;
 };