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

ui/ui_api.h

Index: ui/ui_api.h
===================================================================
--- ui/ui_api.h	(revision 0)
+++ ui/ui_api.h	(revision 0)
@@ -0,0 +1,29 @@
+// 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_UI_API_H_
+#define UI_UI_API_H_
+#pragma once
+
+// Defines UI_API so that funtionality implemented by the UI module can be
+// exported to consumers.
+
+#if defined(COMPONENT_BUILD)
+#if defined(WIN32)
+
+#if defined(UI_IMPLEMENTATION)
+#define UI_API __declspec(dllexport)
+#else
+#define UI_API __declspec(dllimport)
+#endif  // defined(UI_BASE_IMPLEMENTATION)
+
+#else  // defined(WIN32)
+#define UI_API __attribute__((visibility("default")))
+#endif
+
+#else  /// defined(COMPONENT_BUILD)
+#define UI_API
+#endif
+
+#endif  // UI_UI_API_H_