Gtk3 ui: Add libgtk3ui as a separate build component

chrome/browser/ui/libgtkui/gtk2_status_icon.h

 // Copyright 2014 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_GTK2_STATUS_ICON_H_
-#define CHROME_BROWSER_UI_LIBGTK2UI_GTK2_STATUS_ICON_H_
+#ifndef CHROME_BROWSER_UI_LIBGTKUI_GTK2_STATUS_ICON_H_
+#define CHROME_BROWSER_UI_LIBGTKUI_GTK2_STATUS_ICON_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
-#include "chrome/browser/ui/libgtk2ui/gtk2_signal.h"
+#include "chrome/browser/ui/libgtkui/gtk2_signal.h"
 #include "ui/base/glib/glib_integers.h"
 #include "ui/base/glib/glib_signal.h"
 #include "ui/views/linux_ui/status_icon_linux.h"
 
 typedef struct _GtkStatusIcon GtkStatusIcon;
 
 namespace gfx {
 class ImageSkia;
 }
 
 namespace ui {
 class MenuModel;
 }
 
-namespace libgtk2ui {
+namespace libgtkui {
 class AppIndicatorIconMenu;
 
 // Status icon implementation which uses the system tray X11 spec (via
 // GtkStatusIcon).
 class Gtk2StatusIcon : public views::StatusIconLinux {
  public:
   Gtk2StatusIcon(const gfx::ImageSkia& image, const base::string16& tool_tip);
   ~Gtk2StatusIcon() override;
 
   // Overridden from views::StatusIconLinux:
@@ skipping 12 matching lines @@
                      guint,
                      guint);
 
   GtkStatusIcon* gtk_status_icon_;
 
   std::unique_ptr<AppIndicatorIconMenu> menu_;
 
   DISALLOW_COPY_AND_ASSIGN(Gtk2StatusIcon);
 };
 
-}  // namespace libgtk2ui
+}  // namespace libgtkui
 
-#endif  // CHROME_BROWSER_UI_LIBGTK2UI_GTK2_STATUS_ICON_H_
+#endif  // CHROME_BROWSER_UI_LIBGTKUI_GTK2_STATUS_ICON_H_