Return unique_ptr from WebClient::CreateWebMainParts()

ios/web/public/web_client.mm

 // 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.
 
 #import "ios/web/public/web_client.h"
 
 #import <Foundation/Foundation.h>
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ skipping 10 matching lines @@
 WebClient* GetWebClient() {
   return g_client;
 }
 
 WebClient::WebClient() {
 }
 
 WebClient::~WebClient() {
 }
 
-WebMainParts* WebClient::CreateWebMainParts() {
+std::unique_ptr<WebMainParts> WebClient::CreateWebMainParts() {
   return nullptr;
 }
 
 std::string WebClient::GetAcceptLangs(BrowserState* state) const {
   return std::string();
 }
 
 std::string WebClient::GetApplicationLocale() const {
   return "en-US";
 }
@@ skipping 40 matching lines @@
     WebState* web_state,
     int cert_error,
     const net::SSLInfo& ssl_info,
     const GURL& request_url,
     bool overridable,
     const base::Callback<void(bool)>& callback) {
   callback.Run(false);
 }
 
 }  // namespace web