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

components/sync/driver/generic_change_processor.cc

Index: components/sync/driver/generic_change_processor.cc
diff --git a/components/sync/driver/generic_change_processor.cc b/components/sync/driver/generic_change_processor.cc
index 92244875a730ccf477bbcd088e7f54d62ca22154..1dee59fda337dfbdee48bb11ed9df1a63826b28d 100644
--- a/components/sync/driver/generic_change_processor.cc
+++ b/components/sync/driver/generic_change_processor.cc
@@ -16,6 +16,7 @@
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "components/sync/base/unrecoverable_error_handler.h"
 #include "components/sync/driver/sync_api_component_factory.h"
+#include "components/sync/driver/sync_client.h"
 #include "components/sync/model/local_change_observer.h"
 #include "components/sync/model/sync_change.h"
 #include "components/sync/model/sync_error.h"
@@ -110,7 +111,7 @@
     const base::WeakPtr<SyncableService>& local_service,
     const base::WeakPtr<SyncMergeResult>& merge_result,
     UserShare* user_share,
-    SyncApiComponentFactory* driver_factory,
+    SyncClient* sync_client,
     std::unique_ptr<AttachmentStoreForSync> attachment_store)
     : ChangeProcessor(std::move(error_handler)),
       type_(type),
@@ -126,8 +127,10 @@
       ReadTransaction trans(FROM_HERE, share_handle());
       store_birthday = trans.GetStoreBirthday();
     }
-    attachment_service_ = driver_factory->CreateAttachmentService(
-        std::move(attachment_store), *user_share, store_birthday, type, this);
+    attachment_service_ =
+        sync_client->GetSyncApiComponentFactory()->CreateAttachmentService(
+            std::move(attachment_store), *user_share, store_birthday, type,
+            this);
     attachment_service_weak_ptr_factory_ =
         base::MakeUnique<base::WeakPtrFactory<AttachmentService>>(
             attachment_service_.get());