Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtk2ui/libgtk2ui_export.h

Index: chrome/browser/ui/libgtk2ui/libgtk2ui_export.h
diff --git a/chrome/browser/ui/libgtk2ui/libgtk2ui_export.h b/chrome/browser/ui/libgtk2ui/libgtk2ui_export.h
deleted file mode 100644
index 78e71e229b4c1486fa7cf32a9bdbfca8ded69bce..0000000000000000000000000000000000000000
--- a/chrome/browser/ui/libgtk2ui/libgtk2ui_export.h
+++ /dev/null
@@ -1,28 +0,0 @@
-// Copyright (c) 2012 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 CHROME_BROWSER_UI_LIBGTK2UI_LIBGTK2UI_EXPORT_H_
-#define CHROME_BROWSER_UI_LIBGTK2UI_LIBGTK2UI_EXPORT_H_
-
-// Defines LIBGTK2UI_EXPORT so that functionality implemented by our limited
-// gtk2 module can be exported to consumers.
-
-#if defined(COMPONENT_BUILD)
-#if defined(WIN32)
-
-#error "LIBGTK2UI does not build on Windows."
-
-#else  // defined(WIN32)
-#if defined(LIBGTK2UI_IMPLEMENTATION)
-#define LIBGTK2UI_EXPORT __attribute__((visibility("default")))
-#else
-#define LIBGTK2UI_EXPORT
-#endif
-#endif
-
-#else  // defined(COMPONENT_BUILD)
-#define LIBGTK2UI_EXPORT
-#endif
-
-#endif  // CHROME_BROWSER_UI_LIBGTK2UI_LIBGTK2UI_EXPORT_H_