Cleanup: Remove unused SearchTabHelper::GetOpenUrls

chrome/browser/ui/search/search_tab_helper_delegate.cc

 // Copyright 2014 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/search/search_tab_helper_delegate.h"
 
 void SearchTabHelperDelegate::OnWebContentsInstantSupportDisabled(
     const content::WebContents* web_contents) {
 }
 
 OmniboxView* SearchTabHelperDelegate::GetOmniboxView() {
-  return NULL;
-}
-
-std::set<std::string> SearchTabHelperDelegate::GetOpenUrls() {
-  return std::set<std::string>();
+  return nullptr;
 }
 
 SearchTabHelperDelegate::~SearchTabHelperDelegate() {
 }