[KeyboardEvent] Use DOM |code| rather than Windows-based key code

ui/events/keycodes/keyboard_codes_win.h

 // 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.
 
 #ifndef UI_EVENTS_KEYCODES_KEYBOARD_CODES_WIN_H_
 #define UI_EVENTS_KEYCODES_KEYBOARD_CODES_WIN_H_
 
 #include <windows.h>
 #include <ime.h>
 
@@ skipping 164 matching lines @@
   VKEY_CRSEL = VK_CRSEL,
   VKEY_EXSEL = VK_EXSEL,
   VKEY_EREOF = VK_EREOF,
   VKEY_PLAY = VK_PLAY,
   VKEY_ZOOM = VK_ZOOM,
   VKEY_NONAME = VK_NONAME,
   VKEY_PA1 = VK_PA1,
   VKEY_OEM_CLEAR = VK_OEM_CLEAR,
   VKEY_UNKNOWN = 0,
 
+  // These keys are defined in POSIX but not in Windows
+  VKEY_POWER = VKEY_UNKNOWN,
+  VKEY_BRIGHTNESS_DOWN = VKEY_UNKNOWN,
+  VKEY_BRIGHTNESS_UP = VKEY_UNKNOWN,
+
   // Windows does not have a specific key code for AltGr. We use the unused
   // VK_OEM_AX to represent AltGr, matching the behaviour of Firefox on Linux.
   VKEY_ALTGR = VK_OEM_AX,
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_KEYCODES_KEYBOARD_CODES_WIN_H_