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

chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc

Index: chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc
diff --git a/chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc b/chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc
index ab178b52e14c25f83c2184dbf2e0b07bf7a29830..7ba73eb93e8e16bbb5ef6a77349ee6d2eec858fb 100644
--- a/chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc
+++ b/chrome/browser/ui/gtk/external_protocol_dialog_gtk.cc
@@ -96,8 +96,8 @@ ExternalProtocolDialogGtk::ExternalProtocolDialogGtk(const GURL& url)
                      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);