Introduce ui.dll / libui.so for the component build.

ui/base/keycodes/keyboard_code_conversion_gtk.h

 // Copyright (c) 2011 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.
 
 /*
  * Copyright (C) 2006, 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2006 Michael Emmel mike.emmel@gmail.com
  * Copyright (C) 2007 Holger Hans Peter Freyther
  * Copyright (C) 2008 Collabora, Ltd.  All rights reserved.
  * Copyright (C) 2008, 2009 Google Inc.
@@ skipping 20 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // WindowsKeyCodeForGdkKeyCode is copied from platform/gtk/KeyEventGtk.cpp
 
 #ifndef UI_BASE_KEYCODES_KEYBOARD_CODE_CONVERSION_GTK_H_
 #define UI_BASE_KEYCODES_KEYBOARD_CODE_CONVERSION_GTK_H_
 #pragma once
 
 #include "ui/base/keycodes/keyboard_codes_posix.h"
+#include "ui/ui_api.h"
 
 typedef struct _GdkEventKey GdkEventKey;
 
 namespace ui {
 
-KeyboardCode WindowsKeyCodeForGdkKeyCode(int keycode);
+UI_API KeyboardCode WindowsKeyCodeForGdkKeyCode(int keycode);
 
-int GdkKeyCodeForWindowsKeyCode(KeyboardCode keycode, bool shift);
+UI_API int GdkKeyCodeForWindowsKeyCode(KeyboardCode keycode, bool shift);
 
 KeyboardCode KeyboardCodeFromGdkEventKey(GdkEventKey* event);
 
 } // namespace ui
 
 #endif  // UI_BASE_KEYCODES_KEYBOARD_CODE_CONVERSION_GTK_H_