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

components/browser_sync/profile_sync_components_factory_impl.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_components_factory_impl.h"
 
 #include <utility>
 
 #include "base/debug/dump_without_crashing.h"
 #include "base/feature_list.h"
@@ skipping 295 matching lines @@
   return new DataTypeManagerImpl(debug_info_listener, controllers,
                                  encryption_handler, backend, observer);
 }
 
 syncer::SyncBackendHost*
 ProfileSyncComponentsFactoryImpl::CreateSyncBackendHost(
     const std::string& name,
     invalidation::InvalidationService* invalidator,
     const base::WeakPtr<syncer::SyncPrefs>& sync_prefs,
     const base::FilePath& sync_folder) {
-  return new syncer::SyncBackendHostImpl(name, sync_client_, ui_thread_,
-                                         invalidator, sync_prefs, sync_folder);
+  return new syncer::SyncBackendHostImpl(name, sync_client_, invalidator,
+                                         sync_prefs, sync_folder);
 }
 
 std::unique_ptr<syncer::LocalDeviceInfoProvider>
 ProfileSyncComponentsFactoryImpl::CreateLocalDeviceInfoProvider() {
   return base::MakeUnique<syncer::LocalDeviceInfoProviderImpl>(
       channel_, version_, is_tablet_);
 }
 
 class TokenServiceProvider
     : public OAuth2TokenServiceRequest::TokenServiceProvider {
@@ skipping 102 matching lines @@
 
 // static
 void ProfileSyncComponentsFactoryImpl::OverridePrefsForUssTest(bool use_uss) {
   override_prefs_controller_to_uss_for_test_ = use_uss;
 }
 
 bool ProfileSyncComponentsFactoryImpl::
     override_prefs_controller_to_uss_for_test_ = false;
 
 }  // namespace browser_sync