Factor out uses of the WebContentsModalDialog interface from platform-independent code

chrome/browser/ui/webui/certificate_viewer_webui.cc

 // Copyright (c) 2012 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/webui/certificate_viewer_webui.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/i18n/time_formatting.h"
 #include "base/json/json_writer.h"
@@ skipping 57 matching lines @@
 }
 
 void CertificateViewerDialog::Show(WebContents* web_contents,
                                    gfx::NativeWindow parent) {
   // TODO(bshe): UI tweaks needed for Aura HTML Dialog, such as adding padding
   // on the title for Aura ConstrainedWebDialogUI.
   window_ = CreateConstrainedWebDialog(
       web_contents->GetBrowserContext(),
       this,
       NULL,
-      web_contents)->GetWindow()->GetNativeDialog();
+      web_contents)->GetNativeWindow();
 }
 
 ui::ModalType CertificateViewerDialog::GetDialogModalType() const {
   return ui::MODAL_TYPE_NONE;
 }
 
 string16 CertificateViewerDialog::GetDialogTitle() const {
   return title_;
 }
 
@@ skipping 314 matching lines @@
     const base::ListValue* args) const {
   int cert_index;
   double val;
   if (!(args->GetDouble(0, &val)))
     return -1;
   cert_index = static_cast<int>(val);
   if (cert_index < 0 || cert_index >= static_cast<int>(cert_chain_.size()))
     return -1;
   return cert_index;
 }