Switch base::Value typemapping to be by value instead of by unique_ptr.

components/safe_json/safe_json_parser_impl.h

 // Copyright 2013 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 COMPONENTS_SAFE_JSON_SAFE_JSON_PARSER_IMPL_H_
 #define COMPONENTS_SAFE_JSON_SAFE_JSON_PARSER_IMPL_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 21 matching lines @@
  private:
   ~SafeJsonParserImpl() override;
 
   // SafeJsonParser implementation.
   void Start() override;
 
   void StartOnIOThread();
   void OnConnectionError();
 
   // mojom::SafeJsonParser::Parse callback.
-  void OnParseDone(std::unique_ptr<base::Value> result,
+  void OnParseDone(const base::Optional<base::Value>& result,
                    const base::Optional<std::string>& error);
 
   // Reports the result on the calling task runner via the |success_callback_|
   // or the |error_callback_|.
   void ReportResults(std::unique_ptr<base::Value> parsed_json,
                      const std::string& error);
 
   const std::string unsafe_json_;
   SuccessCallback success_callback_;
   ErrorCallback error_callback_;
   scoped_refptr<base::SequencedTaskRunner> caller_task_runner_;
 
   std::unique_ptr<content::UtilityProcessMojoClient<mojom::SafeJsonParser>>
       mojo_json_parser_;
 
   // Used instead of DCHECK_CURRENTLY_ON(BrowserThread::IO) because it's
   // posssible that it fails when the IO thread message loop is shutting down.
   // This happens after the IO thread has unregistered from the BrowserThread
   // list.
   base::ThreadChecker io_thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(SafeJsonParserImpl);
 };
 
 }  // namespace safe_json
 
 #endif  // COMPONENTS_SAFE_JSON_SAFE_JSON_PARSER_IMPL_H_