Create MouseWheelEvent directly instead of through MouseEvent.

ui/events/event_unittest.cc

 // Copyright (c) 2012 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/event.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 720 matching lines @@
   ui::TouchEvent touch_event_copy(touch_event);
   EXPECT_EQ(touch_event.pointer_details(), touch_event_copy.pointer_details());
 }
 
 TEST(EventTest, PointerEventCanConvertFrom) {
   const gfx::Point point;
   const base::TimeTicks time;
 
   // Common mouse events can be converted.
   const EventType mouse_allowed[] = {
-      ET_MOUSE_PRESSED, ET_MOUSE_DRAGGED,         ET_MOUSE_MOVED,
-      ET_MOUSE_ENTERED, ET_MOUSE_EXITED,          ET_MOUSE_RELEASED,
-      ET_MOUSEWHEEL,    ET_MOUSE_CAPTURE_CHANGED,
+      ET_MOUSE_PRESSED,         ET_MOUSE_DRAGGED, ET_MOUSE_MOVED,
+      ET_MOUSE_ENTERED,         ET_MOUSE_EXITED,  ET_MOUSE_RELEASED,
+      ET_MOUSE_CAPTURE_CHANGED,
   };
   for (size_t i = 0; i < arraysize(mouse_allowed); i++) {
     MouseEvent event(mouse_allowed[i], point, point, time, 0, 0);
     EXPECT_TRUE(PointerEvent::CanConvertFrom(event));
   }
+  // Mouse wheel events can be converted.
+  MouseWheelEvent event(gfx::Vector2d(), point, point, time, 0, 0);
+  EXPECT_TRUE(PointerEvent::CanConvertFrom(event));
 
   // Common touch events can be converted.
   const EventType touch_allowed[] = {
       ET_TOUCH_PRESSED,
       ET_TOUCH_MOVED,
       ET_TOUCH_RELEASED,
       ET_TOUCH_CANCELLED
   };
   for (size_t i = 0; i < arraysize(touch_allowed); i++) {
     TouchEvent event(touch_allowed[i], point, 0, time);
@@ skipping 251 matching lines @@
   XButtonEvent* button_event = &(native_event.xbutton);
   button_event->type = ButtonPress;
   button_event->button = 4; // A valid wheel button number between min and max.
   MouseWheelEvent mouse_ev(&native_event);
 
   histogram_tester.ExpectTotalCount("Event.Latency.OS.MOUSE_WHEEL", 1);
 #endif
 }
 
 }  // namespace ui