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

ui/base/gtk/gtk_im_context_util.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.
 
 #ifndef UI_BASE_GTK_GTK_IM_CONTEXT_UTIL_H_
 #define UI_BASE_GTK_GTK_IM_CONTEXT_UTIL_H_
 #pragma once
 
 #include <pango/pango-attributes.h>
 
+#include "ui/ui_api.h"
+
 namespace ui {
 
 struct CompositionText;
 
 // Extracts composition text information (text, underlines, selection range)
 // from given Gtk preedit data (utf-8 text, pango attributes, cursor position).
-void ExtractCompositionTextFromGtkPreedit(const gchar* utf8_text,
-                                          PangoAttrList* attrs,
-                                          int cursor_position,
-                                          CompositionText* composition);
+UI_API void ExtractCompositionTextFromGtkPreedit(const gchar* utf8_text,
+                                                 PangoAttrList* attrs,
+                                                 int cursor_position,
+                                                 CompositionText* composition);
 
 }  // namespace ui
 
 #endif  // UI_BASE_GTK_GTK_IM_CONTEXT_UTIL_H_