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

chrome/browser/ui/gtk/certificate_viewer.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 <gtk/gtk.h>
 
 #include <algorithm>
 #include <vector>
 
 #include "base/i18n/time_formatting.h"
@@ skipping 130 matching lines @@
           IDS_CERT_INFO_DIALOG_TITLE,
           UTF8ToUTF16(
               x509_certificate_model::GetTitle(
                   cert_chain_list_.front()))).c_str(),
       parent,
       // Non-modal.
       GTK_DIALOG_NO_SEPARATOR,
       GTK_STOCK_CLOSE,
       GTK_RESPONSE_CLOSE,
       NULL);
-  gtk_box_set_spacing(GTK_BOX(GTK_DIALOG(dialog_)->vbox),
-                      ui::kContentAreaSpacing);
+
+  GtkWidget* content_area = gtk_dialog_get_content_area(GTK_DIALOG(dialog_));
+  gtk_box_set_spacing(GTK_BOX(content_area), ui::kContentAreaSpacing);
 
   x509_certificate_model::RegisterDynamicOids();
   InitGeneralPage();
   InitDetailsPage();
 
   notebook_ = gtk_notebook_new();
   gtk_container_add(GTK_CONTAINER(GTK_DIALOG(dialog_)->vbox), notebook_);
 
   gtk_notebook_append_page(
       GTK_NOTEBOOK(notebook_),
@@ skipping 549 matching lines @@
                                  net::X509Certificate::OSCertHandle cert) {
   net::X509Certificate::OSCertHandles cert_chain;
   x509_certificate_model::GetCertChainFromCert(cert, &cert_chain);
   (new CertificateViewer(parent, cert_chain))->Show();
 }
 
 void ShowNativeCertificateViewer(gfx::NativeWindow parent,
                                  net::X509Certificate* cert) {
   ShowNativeCertificateViewer(parent, cert->os_cert_handle());
 }