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

ui/base/gtk/event_synthesis_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.
 //
 // This file declares routines for creating fake GDK events (at the moment,
 // only keyboard events). This is useful for a variety of testing purposes.
 // NOTE: This should not be used outside of testing.
 
 #ifndef UI_BASE_GTK_EVENT_SYNTHESIS_GTK_
 #define UI_BASE_GTK_EVENT_SYNTHESIS_GTK_
 #pragma once
 
 #include <gdk/gdk.h>
 #include <gdk/gdkkeysyms.h>
 #include <vector>
 
 #include "ui/base/keycodes/keyboard_codes.h"
+#include "ui/ui_api.h"
 
 namespace ui {
 
 // Creates and returns a key event. Passes ownership to the caller.
 GdkEvent* SynthesizeKeyEvent(GdkWindow* event_window,
                              bool press,
                              guint gdk_key,
                              guint state);
 
 // Creates the proper sequence of key events for a key press + release.
 // Ownership of the events in the vector is passed to the caller.
-void SynthesizeKeyPressEvents(
+UI_API void SynthesizeKeyPressEvents(
     GdkWindow* window,
     KeyboardCode key,
     bool control, bool shift, bool alt,
     std::vector<GdkEvent*>* events);
 
 }  // namespace ui
 
 #endif  // UI_BASE_GTK_EVENT_SYNTHESIS_GTK_