Inject JSON parsing in WebResource as a callback rather than inheritance

ios/chrome/browser/web_resource/ios_web_resource_service.cc

-// 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.
-
-#include "ios/chrome/browser/web_resource/ios_web_resource_service.h"
-
-#include "base/bind.h"
-#include "base/json/json_reader.h"
-#include "base/values.h"
-#include "ios/chrome/browser/application_context.h"
-#include "ios/web/public/web_thread.h"
-
-namespace {
-
-const char kInvalidDataTypeError[] =
-    "Data from web resource server is missing or not valid JSON.";
-
-const char kUnexpectedJSONFormatError[] =
-    "Data from web resource server does not have expected format.";
-
-// Helper method to run a closure.
-void RunClosure(const base::Closure& closure) {
-  closure.Run();
-}
-
-}  // namespace
-
-IOSWebResourceService::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)
-    : web_resource::WebResourceService(
-          prefs,
-          web_resource_server,
-          apply_locale_to_url ? GetApplicationContext()->GetApplicationLocale()
-                              : std::string(),
-          last_update_time_pref_name,
-          start_fetch_delay_ms,
-          cache_update_delay_ms,
-          GetApplicationContext()->GetSystemURLRequestContext(),
-          nullptr) {
-}
-
-IOSWebResourceService::~IOSWebResourceService() {
-}
-
-// static
-base::Closure IOSWebResourceService::ParseJSONOnBackgroundThread(
-    const std::string& data,
-    const SuccessCallback& success_callback,
-    const ErrorCallback& error_callback) {
-  if (data.empty())
-    return base::Bind(error_callback, std::string(kInvalidDataTypeError));
-
-  scoped_ptr<base::Value> value(base::JSONReader::Read(data));
-  if (!value.get()) {
-    // Page information not properly read, or corrupted.
-    return base::Bind(error_callback, std::string(kInvalidDataTypeError));
-  }
-
-  if (!value->IsType(base::Value::TYPE_DICTIONARY))
-    return base::Bind(error_callback, std::string(kUnexpectedJSONFormatError));
-
-  return base::Bind(success_callback, base::Passed(&value));
-}
-
-void IOSWebResourceService::ParseJSON(const std::string& data,
-                                      const SuccessCallback& success_callback,
-                                      const ErrorCallback& error_callback) {
-  base::PostTaskAndReplyWithResult(
-      web::WebThread::GetBlockingPool(), FROM_HERE,
-      base::Bind(&IOSWebResourceService::ParseJSONOnBackgroundThread, data,
-                 success_callback, error_callback),
-      base::Bind(&RunClosure));
-}