Migrate SequencedTaskRunnerHandle calls to TaskRunnerHandle calls.

components/safe_json/safe_json_parser.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_H_
 #define COMPONENTS_SAFE_JSON_SAFE_JSON_PARSER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 
 namespace base {
 class Value;
 }
 
 namespace safe_json {
 
 // SafeJsonParser parses a given JSON safely via a platform-dependent mechanism
 // (like parsing it in a utility process or in a memory-safe environment).
 // Internally, an instance of this class is created when Parse() is called and
-// is kept alive until one of the two callbacks is called, after which it
-// deletes itself.
+// is kept alive until one of the two callbacks is executed on the original
+// caller's TaskRunner, after which it deletes itself.
 class SafeJsonParser {
  public:
   using SuccessCallback = base::Callback<void(std::unique_ptr<base::Value>)>;
   using ErrorCallback = base::Callback<void(const std::string&)>;
 
   using Factory = SafeJsonParser* (*)(const std::string& unsafe_json,
                                       const SuccessCallback& success_callback,
                                       const ErrorCallback& error_callback);
 
   // Starts parsing the passed in |unsafe_json| and calls either
   // |success_callback| or |error_callback| when finished.
   static void Parse(const std::string& unsafe_json,
                     const SuccessCallback& success_callback,
                     const ErrorCallback& error_callback);
 
   static void SetFactoryForTesting(Factory factory);
 
  protected:
   virtual ~SafeJsonParser() {}
 
  private:
   virtual void Start() = 0;
 };
 
 }  // namespace safe_json
 
 #endif  // COMPONENTS_SAFE_JSON_SAFE_JSON_PARSER_H_