infobars: Remove the downcast AsAlternateNavInfoBarDelegate() function.

chrome/browser/ui/omnibox/alternate_nav_infobar_delegate.cc

 // Copyright 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/omnibox/alternate_nav_infobar_delegate.h"
 
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/api/infobars/infobar_service.h"
 #include "content/public/browser/web_contents.h"
 #include "grit/generated_resources.h"
@@ skipping 38 matching lines @@
       // the future.
       content::PAGE_TRANSITION_TYPED,
       false);
   owner()->GetWebContents()->OpenURL(params);
 
   // We should always close, even if the navigation did not occur within this
   // WebContents.
   return true;
 }
 
-AlternateNavInfoBarDelegate*
-    AlternateNavInfoBarDelegate::AsAlternateNavInfoBarDelegate() {
-  return this;
-}
-
 gfx::Image* AlternateNavInfoBarDelegate::GetIcon() const {
   return &ui::ResourceBundle::GetSharedInstance().GetNativeImageNamed(
       IDR_INFOBAR_ALT_NAV_URL);
 }
 
 InfoBarDelegate::Type AlternateNavInfoBarDelegate::GetInfoBarType() const {
   return PAGE_ACTION_TYPE;
 }