During upgrade to the Chromium 61 we have switched from GTK2 to GTK3
and now we have a few warnings about stuff being deprecated in GTK3.
Check any Linux build to get a list of them.

/cc @zcbenz 
atom/browser/ui/message_box_gtk.cc
public:
  GtkMessageBox(NativeWindow* parent_window,
                MessageBoxType type,
                const std::vector<std::string>& buttons,
                int default_id,
                int cancel_id,
                const std::string& title,
                const std::string& message,
                const std::string& detail,
                const std::string& checkbox_label,
                bool checkbox_checked,
                const gfx::ImageSkia& icon)
      : cancel_id_(cancel_id),
        checkbox_checked_(false),
        parent_(static_cast<NativeWindow*>(parent_window)) {
    
    dialog_ = gtk_message_dialog_new(
        nullptr,  
        static_cast<GtkDialogFlags>(0),  
        GetMessageType(type),  
        GTK_BUTTONS_NONE,  
        "%s", message.c_str());
    if (!detail.empty())
      gtk_message_dialog_format_secondary_text(
          GTK_MESSAGE_DIALOG(dialog_), "%s", detail.c_str());
    if (!title.empty())
      gtk_window_set_title(GTK_WINDOW(dialog_), title.c_str());
    
    if (!icon.isNull()) {
      GdkPixbuf* pixbuf = libgtkui::GdkPixbufFromSkBitmap(*icon.bitmap());