Generate correct KeyboardCode (VKEY).

ui/events/ozone/layout/xkb/xkb_key_code_converter.h

 // Copyright 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_OZONE_LAYOUT_XKB_XKB_KEY_CODE_CONVERTER_H_
 #define UI_EVENTS_OZONE_LAYOUT_XKB_XKB_KEY_CODE_CONVERTER_H_
 
 #include <xkbcommon/xkbcommon.h>
 
 namespace ui {
 
 enum class DomCode;
 
+// XKB scan code values are platform-dependent; this provides the layout engine
+// with the mapping from DomCode to xkb_keycode_t. (This mapping is in principle
+// derivable from the XKB keyboard layout, but xkbcommon does not provide a
+// practical interface to do so.)
 class EVENTS_OZONE_LAYOUT_EXPORT XkbKeyCodeConverter {
  public:
   XkbKeyCodeConverter();
   virtual ~XkbKeyCodeConverter();
   xkb_keycode_t InvalidXkbKeyCode() const { return invalid_xkb_keycode_; }
   virtual xkb_keycode_t DomCodeToXkbKeyCode(DomCode dom_code) const = 0;
 
  protected:
   xkb_keycode_t invalid_xkb_keycode_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_OZONE_LAYOUT_XKB_XKB_KEY_CODE_CONVERTER_H_