[Sync] Switch ModelTypeStore* from blocking pool to post_task.h

ios/chrome/browser/reading_list/reading_list_model_factory.cc

 // Copyright 2016 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/reading_list/reading_list_model_factory.h"
 
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "base/memory/ptr_util.h"
@@ skipping 45 matching lines @@
       PrefRegistry::NO_REGISTRATION_FLAGS);
 }
 
 std::unique_ptr<KeyedService> ReadingListModelFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* chrome_browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
 
   const syncer::ModelTypeStoreFactory& store_factory =
       browser_sync::ProfileSyncService::GetModelTypeStoreFactory(
-          syncer::READING_LIST, chrome_browser_state->GetStatePath(),
-          web::WebThread::GetBlockingPool());
+          syncer::READING_LIST, chrome_browser_state->GetStatePath());
   std::unique_ptr<ReadingListStore> store = base::MakeUnique<ReadingListStore>(
       store_factory,
       base::Bind(&syncer::ModelTypeChangeProcessor::Create,
                  base::BindRepeating(&syncer::ReportUnrecoverableError,
                                      GetChannel())));
 
   std::unique_ptr<KeyedService> reading_list_model =
       base::MakeUnique<ReadingListModelImpl>(
           std::move(store), chrome_browser_state->GetPrefs(),
           base::MakeUnique<base::DefaultClock>());
   return reading_list_model;
 }
 
 web::BrowserState* ReadingListModelFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
   return GetBrowserStateRedirectedInIncognito(context);
 }