Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtkui/chrome_gtk_menu_subclasses.h

 // Copyright 2013 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_CHROME_GTK_MENU_SUBCLASSES_H_
-#define CHROME_BROWSER_UI_LIBGTK2UI_CHROME_GTK_MENU_SUBCLASSES_H_
+#ifndef CHROME_BROWSER_UI_LIBGTKUI_CHROME_GTK_MENU_SUBCLASSES_H_
+#define CHROME_BROWSER_UI_LIBGTKUI_CHROME_GTK_MENU_SUBCLASSES_H_
 
 #include <gtk/gtk.h>
 
 // This file declares two subclasses of Gtk's menu classes. We do this because
 // when we were a GTK app proper, we had classes with the same names, and gtk
 // theme authors started writing themes and styling chrome's menus by targeting
 // these classes. We have to fetch our colors from these theme classes in
 // specific because several newer GTK+2 themes are pixmap based and they
 // specifically give real colors only to these classes.
 
@@ skipping 20 matching lines @@
 };
 
 struct _GtkCustomMenuItemClass {
   GtkMenuItemClass parent_class;
 };
 
 GtkWidget* gtk_custom_menu_item_new();
 
 G_END_DECLS
 
-#endif  // CHROME_BROWSER_UI_LIBGTK2UI_CHROME_GTK_MENU_SUBCLASSES_H_
+#endif  // CHROME_BROWSER_UI_LIBGTKUI_CHROME_GTK_MENU_SUBCLASSES_H_