event_utils_win_unittest.cc: add missing override

ui/events/win/event_utils_win_unittest.cc

 // Copyright 2016 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_utils.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/win/window_impl.h"
 
 namespace ui {
 
 namespace {
 
 class TestWindow : public gfx::WindowImpl {
  public:
   TestWindow() {}
   ~TestWindow() override {}
 
   BOOL ProcessWindowMessage(HWND window,
                             UINT message,
                             WPARAM w_param,
                             LPARAM l_param,
                             LRESULT& result,
-                            DWORD msg_map_id = 0) {
+                            DWORD msg_map_id = 0) override {
     return true;
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TestWindow);
 };
 
 MSG CreateEvent(UINT type, WORD x, WORD y, HWND hwnd) {
   MSG event;
   event.message = type;
@@ skipping 22 matching lines @@
   }
 
   MSG event = CreateEvent(WM_LBUTTONDOWN, x_coord, y_coord, test_window.hwnd());
   EXPECT_EQ(gfx::Point(x_coord + x_window_offset, y_coord + y_window_offset),
             EventSystemLocationFromNative(event));
 }
 
 }  // namespace
 
 }  // namespace ui