gtk: Use gtk_dialog_get_content_area() throughout.

chrome/browser/ui/gtk/extensions/extension_install_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 <gtk/gtk.h>
 
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/extensions/extension_install_dialog.h"
 #include "chrome/browser/profiles/profile.h"
@@ skipping 56 matching lines @@
       GTK_DIALOG(dialog),
       cancel > 0 ? l10n_util::GetStringUTF8(cancel).c_str(): GTK_STOCK_CANCEL,
       GTK_RESPONSE_CLOSE);
   gtk_dialog_add_button(
       GTK_DIALOG(dialog),
       l10n_util::GetStringUTF8(ExtensionInstallUI::kButtonIds[type]).c_str(),
       GTK_RESPONSE_ACCEPT);
   gtk_dialog_set_has_separator(GTK_DIALOG(dialog), FALSE);
 
   // Create a two column layout.
-  GtkWidget* content_area = GTK_DIALOG(dialog)->vbox;
+  GtkWidget* content_area = gtk_dialog_get_content_area(GTK_DIALOG(dialog));
   gtk_box_set_spacing(GTK_BOX(content_area), gtk_util::kContentAreaSpacing);
 
   GtkWidget* icon_hbox = gtk_hbox_new(FALSE, gtk_util::kContentAreaSpacing);
   gtk_box_pack_start(GTK_BOX(content_area), icon_hbox, TRUE, TRUE, 0);
 
   // Resize the icon if necessary.
   SkBitmap scaled_icon = *skia_icon;
   if (scaled_icon.width() > kImageSize || scaled_icon.height() > kImageSize) {
     scaled_icon = skia::ImageOperations::Resize(scaled_icon,
         skia::ImageOperations::RESIZE_LANCZOS3,
@@ skipping 100 matching lines @@
   BrowserWindowGtk* browser_window = static_cast<BrowserWindowGtk*>(
       browser->window());
   if (!browser_window) {
     delegate->InstallUIAbort(false);
     return;
   }
 
   ShowInstallDialog(
       browser_window->window(), icon, extension, delegate, permissions, type);
 }