[Sync] Convert NonBlockingDataTypeController to be single-thread.

chrome/browser/sync/chrome_sync_client.cc

Index: chrome/browser/sync/chrome_sync_client.cc
diff --git a/chrome/browser/sync/chrome_sync_client.cc b/chrome/browser/sync/chrome_sync_client.cc
index a4dabfeb395052c99aadb321902b05ecf2c2184d..56882d9d80f0b8ec6631e8bcf777eaa75736fe59 100644
--- a/chrome/browser/sync/chrome_sync_client.cc
+++ b/chrome/browser/sync/chrome_sync_client.cc
@@ -425,15 +425,16 @@ ChromeSyncClient::GetSyncableServiceForType(syncer::ModelType type) {
   }
 }
 
-syncer_v2::ModelTypeService* ChromeSyncClient::GetModelTypeServiceForType(
-    syncer::ModelType type) {
+base::WeakPtr<syncer_v2::ModelTypeService>
+ChromeSyncClient::GetModelTypeServiceForType(syncer::ModelType type) {
   switch (type) {
     case syncer::DEVICE_INFO:
       return ProfileSyncServiceFactory::GetForProfile(profile_)
-          ->GetDeviceInfoService();
+          ->GetDeviceInfoService()
+          ->AsWeakPtr();
     default:
       NOTREACHED();
-      return nullptr;
+      return base::WeakPtr<syncer_v2::ModelTypeService>();
   }
 }