[Sync] Pass a TaskRunner into SBHI/SBHC, not a thread or message loop.

components/browser_sync/profile_sync_service.cc

 // Copyright (c) 2012 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 "components/browser_sync/profile_sync_service.h"
 
 #include <stddef.h>
 
 #include <cstddef>
 #include <map>
@@ skipping 525 matching lines @@
       local_sync_backend_folder.Append(kLoopbackServerBackendFilename);
 #endif  // defined(OS_WIN)
 
   SyncBackendHost::HttpPostProviderFactoryGetter
       http_post_provider_factory_getter =
           base::Bind(&syncer::NetworkResources::GetHttpPostProviderFactory,
                      base::Unretained(network_resources_.get()),
                      url_request_context_, network_time_update_callback_);
 
   backend_->Initialize(
-      this, sync_thread_.get(), GetJsEventHandler(), sync_service_url_,
+      this, sync_thread_->task_runner(), GetJsEventHandler(), sync_service_url_,
       local_device_->GetSyncUserAgent(), credentials, delete_stale_data,
       enable_local_sync_backend, local_sync_backend_folder,
       base::MakeUnique<syncer::SyncManagerFactory>(),
       MakeWeakHandle(sync_enabled_weak_factory_.GetWeakPtr()),
       base::Bind(syncer::ReportUnrecoverableError, channel_),
       http_post_provider_factory_getter, std::move(saved_nigori_state_));
 }
 
 bool ProfileSyncService::IsEncryptedDatatypeEnabled() const {
   if (encryption_pending())
@@ skipping 1977 matching lines @@
 
   DCHECK(startup_controller_->IsSetupInProgress());
   startup_controller_->SetSetupInProgress(false);
 
   if (IsBackendInitialized())
     ReconfigureDatatypeManager();
   NotifyObservers();
 }
 
 }  // namespace browser_sync