Return unique_ptr from WebClient::CreateWebMainParts()

ios/chrome/browser/web/chrome_web_client.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_WEB_CHROME_WEB_CLIENT_H_
 #define IOS_CHROME_BROWSER_WEB_CHROME_WEB_CLIENT_H_
 
+#include <memory>
+
 #include "base/macros.h"
 #include "ios/web/public/web_client.h"
 
 // Chrome implementation of WebClient.
 class ChromeWebClient : public web::WebClient {
  public:
   ChromeWebClient();
   ~ChromeWebClient() override;
 
   // WebClient implementation.
-  web::WebMainParts* CreateWebMainParts() override;
+  std::unique_ptr<web::WebMainParts> CreateWebMainParts() override;
   void PreWebViewCreation() const override;
   void AddAdditionalSchemes(std::vector<url::SchemeWithType>*
                                 additional_standard_schemes) const override;
   std::string GetAcceptLangs(web::BrowserState* state) const override;
   std::string GetApplicationLocale() const override;
   bool IsAppSpecificURL(const GURL& url) const override;
   base::string16 GetPluginNotSupportedText() const override;
   std::string GetProduct() const override;
   std::string GetUserAgent(bool desktop_user_agent) const override;
   base::string16 GetLocalizedString(int message_id) const override;
@@ skipping 17 matching lines @@
       std::vector<base::SchedulerWorkerPoolParams>* params_vector,
       base::TaskScheduler::WorkerPoolIndexForTraitsCallback*
           index_to_traits_callback) override;
   void PerformExperimentalTaskSchedulerRedirections() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ChromeWebClient);
 };
 
 #endif  // IOS_CHROME_BROWSER_WEB_CHROME_WEB_CLIENT_H_