Create MouseWheelEvent directly instead of through MouseEvent.

ui/events/test/event_generator.cc

 // Copyright 2014 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 "ui/events/test/event_generator.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 148 matching lines @@
 void EventGenerator::PressRightButton() {
   PressButton(ui::EF_RIGHT_MOUSE_BUTTON);
 }
 
 void EventGenerator::ReleaseRightButton() {
   ReleaseButton(ui::EF_RIGHT_MOUSE_BUTTON);
 }
 
 void EventGenerator::MoveMouseWheel(int delta_x, int delta_y) {
   gfx::Point location = GetLocationInCurrentRoot();
-  ui::MouseEvent mouseev(ui::ET_MOUSEWHEEL, location, location,
-                         ui::EventTimeForNow(), flags_, 0);
-  ui::MouseWheelEvent wheelev(mouseev, delta_x, delta_y);
+  ui::MouseWheelEvent wheelev(gfx::Vector2d(delta_x, delta_y), location,
+                              location, ui::EventTimeForNow(), flags_, 0);
   Dispatch(&wheelev);
 }
 
 void EventGenerator::SendMouseEnter() {
   gfx::Point enter_location(current_location_);
   delegate()->ConvertPointToTarget(current_target_, &enter_location);
   ui::MouseEvent mouseev(ui::ET_MOUSE_ENTERED, enter_location, enter_location,
                          ui::EventTimeForNow(), flags_, 0);
   Dispatch(&mouseev);
 }
@@ skipping 510 matching lines @@
   return default_delegate;
 }
 
 EventGeneratorDelegate* EventGenerator::delegate() {
   return const_cast<EventGeneratorDelegate*>(
       const_cast<const EventGenerator*>(this)->delegate());
 }
 
 }  // namespace test
 }  // namespace ui