Async Wheel Event with only the first one cancellable behind a flag.

ui/events/blink/blink_event_util.cc

 // Copyright 2015 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.
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include "ui/events/blink/blink_event_util.h"
 
 #include <stddef.h>
@@ skipping 265 matching lines @@
   float unaccelerated_y =
       GetUnacceleratedDelta(event->delta_y, event->acceleration_ratio_y) +
       GetUnacceleratedDelta(event_to_coalesce.delta_y,
                             event_to_coalesce.acceleration_ratio_y);
   float old_deltaX = event->delta_x;
   float old_deltaY = event->delta_y;
   float old_wheelTicksX = event->wheel_ticks_x;
   float old_wheelTicksY = event->wheel_ticks_y;
   float old_movementX = event->movement_x;
   float old_movementY = event->movement_y;
+  WebInputEvent::DispatchType old_dispatch_type = event->dispatch_type;
   *event = event_to_coalesce;
   event->delta_x += old_deltaX;
   event->delta_y += old_deltaY;
   event->wheel_ticks_x += old_wheelTicksX;
   event->wheel_ticks_y += old_wheelTicksY;
   event->movement_x += old_movementX;
   event->movement_y += old_movementY;
   event->acceleration_ratio_x =
       GetAccelerationRatio(event->delta_x, unaccelerated_x);
   event->acceleration_ratio_y =
       GetAccelerationRatio(event->delta_y, unaccelerated_y);
+  event->dispatch_type =
+      MergeDispatchTypes(old_dispatch_type, event_to_coalesce.dispatch_type);
 }
 
 bool CanCoalesce(const WebTouchEvent& event_to_coalesce,
                  const WebTouchEvent& event) {
   if (event.GetType() != event_to_coalesce.GetType() ||
       event.GetType() != WebInputEvent::kTouchMove ||
       event.GetModifiers() != event_to_coalesce.GetModifiers() ||
       event.touches_length != event_to_coalesce.touches_length ||
       event.touches_length > WebTouchEvent::kTouchesLengthCap)
     return false;
@@ skipping 679 matching lines @@
   switch (type) {
     case blink::WebGestureEvent::kGestureScrollUpdate:
     case blink::WebGestureEvent::kGesturePinchUpdate:
       return true;
     default:
       return false;
   }
 }
 
 }  // namespace ui