Prevent popunders with the new auto-dismissing dialogs.

chrome/browser/ui/javascript_dialogs/javascript_dialog_cocoa.mm

 // Copyright 2016 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/javascript_dialogs/javascript_dialog_cocoa.h"
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/memory/ptr_util.h"
 #include "base/strings/sys_string_conversions.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_alert.h"
@@ skipping 160 matching lines @@
 
 JavaScriptDialogCocoa::JavaScriptDialogCocoa(
     content::WebContents* parent_web_contents,
     content::WebContents* alerting_web_contents,
     const base::string16& title,
     content::JavaScriptMessageType message_type,
     const base::string16& message_text,
     const base::string16& default_prompt_text,
     const content::JavaScriptDialogManager::DialogClosedCallback&
         dialog_callback)
-    : impl_(base::MakeUnique<JavaScriptDialogCocoaImpl>(this,
+    : JavaScriptDialog(parent_web_contents),
+      impl_(base::MakeUnique<JavaScriptDialogCocoaImpl>(this,
                                                         parent_web_contents,
                                                         alerting_web_contents,
                                                         title,
                                                         message_type,
                                                         message_text,
                                                         default_prompt_text,
                                                         dialog_callback)),
       weak_factory_(this) {}