Coalesced mouse wheel event has the position of the most recent event.

content/common/input/event_with_latency_info.cc

 // 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.
 
 #include "content/common/input/event_with_latency_info.h"
 
 #include <bitset>
 #include <limits>
 
 using blink::WebGestureEvent;
@@ skipping 79 matching lines @@
               WebMouseWheelEvent* event) {
   DCHECK(CanCoalesce(event_to_coalesce, *event));
   float unaccelerated_x =
       GetUnacceleratedDelta(event->deltaX, event->accelerationRatioX) +
       GetUnacceleratedDelta(event_to_coalesce.deltaX,
                             event_to_coalesce.accelerationRatioX);
   float unaccelerated_y =
       GetUnacceleratedDelta(event->deltaY, event->accelerationRatioY) +
       GetUnacceleratedDelta(event_to_coalesce.deltaY,
                             event_to_coalesce.accelerationRatioY);
-  event->deltaX += event_to_coalesce.deltaX;
-  event->deltaY += event_to_coalesce.deltaY;
-  event->wheelTicksX += event_to_coalesce.wheelTicksX;
-  event->wheelTicksY += event_to_coalesce.wheelTicksY;
+  float old_deltaX = event->deltaX;
+  float old_deltaY = event->deltaY;
+  float old_wheelTicksX = event->wheelTicksX;
+  float old_wheelTicksY = event->wheelTicksY;
+  float old_movementX = event->movementX;
+  float old_movementY = event->movementY;
+  *event = event_to_coalesce;
+  event->deltaX += old_deltaX;
+  event->deltaY += old_deltaY;
+  event->wheelTicksX += old_wheelTicksX;
+  event->wheelTicksY += old_wheelTicksY;
+  event->movementX += old_movementX;
+  event->movementY += old_movementY;
   event->accelerationRatioX =
       GetAccelerationRatio(event->deltaX, unaccelerated_x);
   event->accelerationRatioY =
       GetAccelerationRatio(event->deltaY, unaccelerated_y);
 }
 
 bool CanCoalesce(const WebTouchEvent& event_to_coalesce,
                  const WebTouchEvent& event) {
   if (event.type != event_to_coalesce.type ||
       event.type != WebInputEvent::TouchMove ||
@@ skipping 171 matching lines @@
 
 const blink::WebInputEvent& ScopedWebInputEventWithLatencyInfo::event() const {
   return *event_;
 }
 
 blink::WebInputEvent& ScopedWebInputEventWithLatencyInfo::event() {
   return *event_;
 }
 
 }  // namespace content