Revise ui::DomKey to unify character and non-character codes.

ui/events/keycodes/keyboard_code_conversion_xkb.h

 // Copyright (c) 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.
 
 #ifndef UI_EVENTS_KEYCODES_KEYBOARD_CODE_CONVERSION_XKB_H_
 #define UI_EVENTS_KEYCODES_KEYBOARD_CODE_CONVERSION_XKB_H_
 
 // These functions are used by X11 targets and by Ozone/XKBcommon targets.
 
 #include "base/strings/string16.h"
 #include "ui/events/events_base_export.h"
+#include "ui/events/keycodes/dom/dom_key.h"
 #include "ui/events/keycodes/xkb_keysym.h"
 
 namespace ui {
 
-enum class DomKey;
-
 // Returns the DomKey associated with a non-character xkb_keysym_t.
 // Returns DomKey::NONE for unrecognized keysyms, which includes
 // all printable characters.
 EVENTS_BASE_EXPORT DomKey NonPrintableXKeySymToDomKey(xkb_keysym_t keysym);
 
 // TODO(kpschoedel) crbug.com/442757
 // Returns the dead key combining character associated with an xkb_keysym_t,
 // or 0 if the keysym is not recognized.
 // base::char16 DeadXKeySymToCombiningCharacter(xkb_keysym_t keysym);
 
 // Return the DomKey determined by the XKB layout result (keysym, character).
 EVENTS_BASE_EXPORT DomKey
 XKeySymToDomKey(xkb_keysym_t keysym, base::char16 character);
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_KEYCODES_KEYBOARD_CODE_CONVERSION_XKB_H_