Return unique_ptr from WebClient::CreateWebMainParts()

ios/web/shell/shell_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/shell/shell_web_client.h"
 
 #import <UIKit/UIKit.h>
 
+#include "base/memory/ptr_util.h"
 #include "ios/web/public/user_agent.h"
 #include "ios/web/shell/shell_web_main_parts.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace web {
 
 ShellWebClient::ShellWebClient() {
 }
 
 ShellWebClient::~ShellWebClient() {
 }
 
-WebMainParts* ShellWebClient::CreateWebMainParts() {
-  web_main_parts_.reset(new ShellWebMainParts);
-  return web_main_parts_.get();
+std::unique_ptr<WebMainParts> ShellWebClient::CreateWebMainParts() {
+  std::unique_ptr<ShellWebMainParts> parts =
+      base::MakeUnique<ShellWebMainParts>();
+  web_main_parts_ = parts.get();
+  return std::move(parts);
 }
 
 ShellBrowserState* ShellWebClient::browser_state() const {
   return web_main_parts_->browser_state();
 }
 
 std::string ShellWebClient::GetProduct() const {
   return "CriOS/36.77.34.45";
 }
 
@@ skipping 27 matching lines @@
                                               block_callback.Run(true);
                                             }]];
   }
   [[UIApplication sharedApplication].keyWindow.rootViewController
       presentViewController:alert
                    animated:YES
                  completion:nil];
 }
 
 }  // namespace web