Inject JSON parsing in WebResource as a callback rather than inheritance

ios/chrome/browser/web_resource/ios_web_resource_service.h

-// Copyright 2015 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_RESOURCE_IOS_WEB_RESOURCE_SERVICE_H_
-#define IOS_CHROME_BROWSER_WEB_RESOURCE_IOS_WEB_RESOURCE_SERVICE_H_
-
-#include <string>
-
-#include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
-#include "components/web_resource/web_resource_service.h"
-
-// iOS implementation of WebResourceService.
-// IOSWebResourceService does not parses JSON out of process, because of
-// platform limitations.
-class IOSWebResourceService : public web_resource::WebResourceService {
- public:
-  IOSWebResourceService(PrefService* prefs,
-                        const GURL& web_resource_server,
-                        bool apply_locale_to_url,
-                        const char* last_update_time_pref_name,
-                        int start_fetch_delay_ms,
-                        int cache_update_delay_ms);
-
- protected:
-  ~IOSWebResourceService() override;
-
- private:
-  // Parses JSON in a background thread.
-  static base::Closure ParseJSONOnBackgroundThread(
-      const std::string& data,
-      const SuccessCallback& success_callback,
-      const ErrorCallback& error_callback);
-
-  // WebResourceService implementation:
-  void ParseJSON(const std::string& data,
-                 const SuccessCallback& success_callback,
-                 const ErrorCallback& error_callback) override;
-
-  DISALLOW_COPY_AND_ASSIGN(IOSWebResourceService);
-};
-
-#endif  // IOS_CHROME_BROWSER_WEB_RESOURCE_IOS_WEB_RESOURCE_SERVICE_H_