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

components/sync/driver/generic_change_processor_unittest.cc

Index: components/sync/driver/generic_change_processor_unittest.cc
diff --git a/components/sync/driver/generic_change_processor_unittest.cc b/components/sync/driver/generic_change_processor_unittest.cc
index 09045cc028c2c9c378c94576af2cb343e860309d..1bc4628e767f9cd7e67294b0b2803eb3de466795 100644
--- a/components/sync/driver/generic_change_processor_unittest.cc
+++ b/components/sync/driver/generic_change_processor_unittest.cc
@@ -124,7 +124,8 @@
 
   SyncGenericChangeProcessorTest()
       : syncable_service_ptr_factory_(&fake_syncable_service_),
-        mock_attachment_service_(nullptr) {}
+        mock_attachment_service_(nullptr),
+        sync_client_(&sync_factory_) {}
 
   void SetUp() override {
     // Use kType by default, but allow test cases to re-initialize with whatever
@@ -166,7 +167,7 @@
         type, base::MakeUnique<DataTypeErrorHandlerMock>(),
         syncable_service_ptr_factory_.GetWeakPtr(),
         merge_result_ptr_factory_->GetWeakPtr(), test_user_share_->user_share(),
-        &sync_factory_, attachment_store->CreateAttachmentStoreForSync());
+        &sync_client_, attachment_store->CreateAttachmentStoreForSync());
     mock_attachment_service_ = sync_factory_.GetMockAttachmentService();
   }
 
@@ -203,6 +204,7 @@
 
   std::unique_ptr<TestUserShare> test_user_share_;
   MockAttachmentService* mock_attachment_service_;
+  FakeSyncClient sync_client_;
   MockSyncApiComponentFactory sync_factory_;
 
   std::unique_ptr<GenericChangeProcessor> change_processor_;