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

content/common/input/event_with_latency_info.cc

Index: content/common/input/event_with_latency_info.cc
diff --git a/content/common/input/event_with_latency_info.cc b/content/common/input/event_with_latency_info.cc
index a2b306b7eaaa71e6683cc6c23f287f498f6891a2..9aec6328399900b210a0efcd39eb50d05d75160b 100644
--- a/content/common/input/event_with_latency_info.cc
+++ b/content/common/input/event_with_latency_info.cc
@@ -97,10 +97,19 @@ void Coalesce(const WebMouseWheelEvent& event_to_coalesce,
       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 =