Create MouseWheelEvent directly instead of through MouseEvent.

content/browser/renderer_host/input/synthetic_gesture_target_aura.cc

 // Copyright 2013 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/browser/renderer_host/input/synthetic_gesture_target_aura.h"
 
 #include <stddef.h>
 
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_view_aura.h"
@@ skipping 41 matching lines @@
     ui::EventDispatchDetails details =
         host->event_processor()->OnEventFromSource(*iter);
     if (details.dispatcher_destroyed)
       break;
   }
 }
 
 void SyntheticGestureTargetAura::DispatchWebMouseWheelEventToPlatform(
       const blink::WebMouseWheelEvent& web_wheel,
       const ui::LatencyInfo&) {
-  ui::MouseEvent mouse_event(ui::ET_MOUSEWHEEL, gfx::Point(), gfx::Point(),
-                             ui::EventTimeForNow(), ui::EF_NONE, ui::EF_NONE);
+  ui::MouseWheelEvent wheel_event(
+      gfx::Vector2d(web_wheel.deltaX, web_wheel.deltaY), gfx::Point(),
+      gfx::Point(), ui::EventTimeForNow(), ui::EF_NONE, ui::EF_NONE);
   gfx::PointF location(web_wheel.x * device_scale_factor_,
                        web_wheel.y * device_scale_factor_);
-  mouse_event.set_location_f(location);
-  mouse_event.set_root_location_f(location);
-  ui::MouseWheelEvent wheel_event(
-      mouse_event, web_wheel.deltaX, web_wheel.deltaY);
+  wheel_event.set_location_f(location);
+  wheel_event.set_root_location_f(location);
 
   aura::Window* window = GetWindow();
   wheel_event.ConvertLocationToTarget(window, window->GetRootWindow());
   ui::EventDispatchDetails details =
       window->GetHost()->event_processor()->OnEventFromSource(&wheel_event);
   if (details.dispatcher_destroyed)
     return;
 }
 
 namespace {
@@ skipping 85 matching lines @@
       ->min_distance_for_pinch_scroll_in_pixels();
 }
 
 aura::Window* SyntheticGestureTargetAura::GetWindow() const {
   aura::Window* window = render_widget_host()->GetView()->GetNativeView();
   DCHECK(window);
   return window;
 }
 
 }  // namespace content