Gtk: Change NULL to nullptr

chrome/browser/ui/libgtkui/gtk_ui.h

 // Copyright (c) 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_LIBGTKUI_GTK_UI_H_
 #define CHROME_BROWSER_UI_LIBGTKUI_GTK_UI_H_
 
 #include <map>
 #include <memory>
 #include <vector>
@@ skipping 160 matching lines @@
   std::unique_ptr<Gtk2KeyBindingsHandler> key_bindings_handler_;
 
   // Objects to notify when the window frame button order changes.
   base::ObserverList<views::WindowButtonOrderObserver> observer_list_;
 
   // Whether we should lower the window on a middle click to the non client
   // area.
   NonClientMiddleClickAction middle_click_action_;
 
   // Used to override the native theme for a window. If no override is provided
-  // or the callback returns NULL, GtkUi will default to a NativeThemeGtk2
+  // or the callback returns nullptr, GtkUi will default to a NativeThemeGtk2
   // instance.
   NativeThemeGetter native_theme_overrider_;
 
   float device_scale_factor_ = 1.0f;
 
   DISALLOW_COPY_AND_ASSIGN(GtkUi);
 };
 
 }  // namespace libgtkui
 
 // Access point to the GTK2 desktop system. This should be the only symbol that
 // is exported in the library; everything else should be used through the
 // interface, because eventually this .so will be loaded through dlopen at
 // runtime so our main binary can conditionally load GTK2 or GTK3 or EFL or
 // QT or whatever.
 LIBGTKUI_EXPORT views::LinuxUI* BuildGtkUi();
 
 #endif  // CHROME_BROWSER_UI_LIBGTKUI_GTK_UI_H_