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

chrome/browser/ui/gtk/html_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/html_dialog_gtk.h"
 
 #include <gtk/gtk.h>
 
 #include "base/property_bag.h"
 #include "base/utf_string_conversions.h"
@@ skipping 185 matching lines @@
       UTF16ToUTF8(delegate_->GetDialogTitle()).c_str(),
       parent_window_,
       flags,
       NULL);
 
   SetDialogStyle();
   gtk_widget_set_name(dialog_, "chrome-html-dialog");
   g_signal_connect(dialog_, "response", G_CALLBACK(OnResponseThunk), this);
 
   tab_contents_container_.reset(new TabContentsContainerGtk(NULL));
-  gtk_box_pack_start(GTK_BOX(GTK_DIALOG(dialog_)->vbox),
+  GtkWidget* content_area = gtk_dialog_get_content_area(GTK_DIALOG(dialog_));
+  gtk_box_pack_start(GTK_BOX(content_area),
                      tab_contents_container_->widget(), TRUE, TRUE, 0);
 
   tab_contents_container_->SetTab(tab_.get());
 
   gfx::Size dialog_size;
   delegate_->GetDialogSize(&dialog_size);
 
   gtk_widget_set_size_request(GTK_WIDGET(tab_contents_container_->widget()),
                               dialog_size.width(),
                               dialog_size.height());
 
   gtk_widget_show_all(dialog_);
 
   return GTK_WINDOW(dialog_);
 }
 
 void HtmlDialogGtk::OnResponse(GtkWidget* dialog, int response_id) {
   OnDialogClosed(std::string());
 }