GTK: More raw struct access removal, this time focusing on GtkDialog.

chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/ui/gtk/external_protocol_dialog_gtk.h"
 
 #include <gtk/gtk.h>
 
 #include <string>
 
@@ skipping 78 matching lines @@
   gtk_util::SetLabelWidth(label, kMessageWidth);
   gtk_box_pack_start(GTK_BOX(vbox), label, TRUE, TRUE, 0);
 
   // Add the checkbox.
   checkbox_ = gtk_check_button_new_with_label(
       l10n_util::GetStringUTF8(IDS_EXTERNAL_PROTOCOL_CHECKBOX_TEXT).c_str());
   gtk_box_pack_start(GTK_BOX(vbox), checkbox_,
                      FALSE, FALSE, 0);
 
   // Add our vbox to the dialog.
-  gtk_box_pack_start(GTK_BOX(GTK_DIALOG(dialog_)->vbox), vbox,
-                     FALSE, FALSE, 0);
+  GtkWidget* content_area = gtk_dialog_get_content_area(GTK_DIALOG(dialog_));
+  gtk_box_pack_start(GTK_BOX(content_area), vbox, FALSE, FALSE, 0);
 
   g_signal_connect(dialog_, "response", G_CALLBACK(OnResponseThunk), this);
 
   gtk_window_set_resizable(GTK_WINDOW(dialog_), FALSE);
   gtk_widget_show_all(dialog_);
 }
 
 ExternalProtocolDialogGtk::~ExternalProtocolDialogGtk() {
 }
 
@@ skipping 13 matching lines @@
   if (response_id == GTK_RESPONSE_ACCEPT) {
     UMA_HISTOGRAM_LONG_TIMES("clickjacking.launch_url",
                              base::TimeTicks::Now() - creation_time_);
 
     ExternalProtocolHandler::LaunchUrlWithoutSecurityCheck(url_);
   }
 
   gtk_widget_destroy(dialog_);
   delete this;
 }