[Sync] ModelTypeStore factory shouldn't require valid PSS to function correctly

components/sync/driver/fake_sync_client.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 "components/sync/driver/fake_sync_client.h"
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
 #include "components/sync/base/extensions_activity.h"
 #include "components/sync/base/sync_prefs.h"
@@ skipping 22 matching lines @@
 
 FakeSyncClient::FakeSyncClient(SyncApiComponentFactory* factory)
     : factory_(factory), sync_service_(base::MakeUnique<FakeSyncService>()) {
   SyncPrefs::RegisterProfilePrefs(pref_service_.registry());
 }
 
 FakeSyncClient::~FakeSyncClient() {}
 
 void FakeSyncClient::Initialize() {}
 
+base::SequencedWorkerPool* FakeSyncClient::GetBlockingPool() {
+  return nullptr;
+}
+
 SyncService* FakeSyncClient::GetSyncService() {
   return sync_service_.get();
 }
 
 PrefService* FakeSyncClient::GetPrefService() {
   return &pref_service_;
 }
 
 base::FilePath FakeSyncClient::GetLocalSyncBackendFolder() {
   return base::FilePath();
@@ skipping 61 matching lines @@
 
 SyncApiComponentFactory* FakeSyncClient::GetSyncApiComponentFactory() {
   return factory_;
 }
 
 void FakeSyncClient::SetModelTypeSyncBridge(ModelTypeSyncBridge* bridge) {
   bridge_ = bridge;
 }
 
 }  // namespace syncer