Properly initial a MSG struct in EventTest.

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 902 matching lines @@
       0, XI_TouchEnd, 5, gfx::Point(30, 30), std::vector<Valuator>());
   TouchEvent touch_end(scoped_xevent);
   histogram_tester.ExpectTotalCount("Event.Latency.OS.TOUCH_RELEASED", 1);
 }
 #endif
 
 // Checks that Event.Latency.OS.MOUSE_WHEEL histogram is computed properly.
 TEST(EventTest, EventLatencyOSMouseWheelHistogram) {
 #if defined(OS_WIN)
   base::HistogramTester histogram_tester;
-  MSG event;
-  event.message = WM_MOUSEWHEEL;
+  MSG event = { nullptr, WM_MOUSEWHEEL, 0, 0 };
   MouseWheelEvent mouseWheelEvent(event);
   histogram_tester.ExpectTotalCount("Event.Latency.OS.MOUSE_WHEEL", 1);
 #elif defined(USE_X11)
   base::HistogramTester histogram_tester;
   DeviceDataManagerX11::CreateInstance();
 
   // Initializes a native event and uses it to generate a MouseWheel event.
   XEvent native_event;
   memset(&native_event, 0, sizeof(XEvent));
   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