[Sync] Stop accessing BrowserContextKeyedServiceFactory on non-UI thread.

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 "base/memory/weak_ptr.h"
 #include "components/sync/base/extensions_activity.h"
 #include "components/sync/base/sync_prefs.h"
 #include "components/sync/driver/fake_sync_service.h"
 
 namespace syncer {
 
+using ServiceProvider = SyncClient::ServiceProvider;
+
 namespace {
 
 void DummyRegisterPlatformTypesCallback(SyncService* sync_service,
                                         ModelTypeSet,
                                         ModelTypeSet) {}
 
+base::WeakPtr<SyncableService> EmptyWeakPtr() {
+  return base::WeakPtr<SyncableService>();
+}
+
 }  // namespace
 
 FakeSyncClient::FakeSyncClient()
     : bridge_(nullptr),
       factory_(nullptr),
       sync_service_(base::MakeUnique<FakeSyncService>()) {
   // Register sync preferences and set them to "Sync everything" state.
   SyncPrefs::RegisterProfilePrefs(pref_service_.registry());
   SyncPrefs sync_prefs(GetPrefService());
   sync_prefs.SetFirstSetupComplete();
@@ skipping 63 matching lines @@
 }
 
 scoped_refptr<ExtensionsActivity> FakeSyncClient::GetExtensionsActivity() {
   return scoped_refptr<ExtensionsActivity>();
 }
 
 sync_sessions::SyncSessionsClient* FakeSyncClient::GetSyncSessionsClient() {
   return nullptr;
 }
 
-base::WeakPtr<SyncableService> FakeSyncClient::GetSyncableServiceForType(
-    ModelType type) {
-  return base::WeakPtr<SyncableService>();
+ServiceProvider FakeSyncClient::GetSyncableServiceForType(ModelType type) {
+  return base::Bind(&EmptyWeakPtr);
 }
 
 base::WeakPtr<ModelTypeSyncBridge> FakeSyncClient::GetSyncBridgeForModelType(
     ModelType type) {
   return bridge_->AsWeakPtr();
 }
 
 scoped_refptr<ModelSafeWorker> FakeSyncClient::CreateModelWorkerForGroup(
     ModelSafeGroup group) {
   return scoped_refptr<ModelSafeWorker>();
 }
 
 SyncApiComponentFactory* FakeSyncClient::GetSyncApiComponentFactory() {
   return factory_;
 }
 
 void FakeSyncClient::SetModelTypeSyncBridge(ModelTypeSyncBridge* bridge) {
   bridge_ = bridge;
 }
 
 }  // namespace syncer