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

chrome/browser/ui/gtk/certificate_viewer.cc

Index: chrome/browser/ui/gtk/certificate_viewer.cc
diff --git a/chrome/browser/ui/gtk/certificate_viewer.cc b/chrome/browser/ui/gtk/certificate_viewer.cc
index f1bb64dd5dbe255f3c0a48c9ad1ac38a629b74b1..fd3d5347d08229da63c0fecb89c61ef4eea803e1 100644
--- a/chrome/browser/ui/gtk/certificate_viewer.cc
+++ b/chrome/browser/ui/gtk/certificate_viewer.cc
@@ -148,8 +148,9 @@ CertificateViewer::CertificateViewer(
       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();