[SyncFS] Make routines using metadata database async

chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc

Index: chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc b/chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc
index 4406b8009e33e6b4dfcc1254745e59a3631a423b..34496834c252f4a2d2efe9a3fa1d920d568951cf 100644
--- a/chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc
+++ b/chrome/browser/sync_file_system/drive_backend/sync_engine_unittest.cc
@@ -136,7 +136,7 @@ class SyncEngineTest
   SyncEngine* sync_engine() { return sync_engine_.get(); }
 
   void UpdateRegisteredApps() {
-    sync_engine_->UpdateRegisteredApps();
+    sync_engine_->UpdateRegisteredAppsForTesting();
   }
 
   SyncTaskManager* GetSyncEngineTaskManager() {
@@ -164,7 +164,8 @@ class SyncEngineTest
 TEST_F(SyncEngineTest, EnableOrigin) {
   FileTracker tracker;
   SyncStatusCode sync_status = SYNC_STATUS_UNKNOWN;
-  MetadataDatabase* metadata_database = sync_engine()->GetMetadataDatabase();
+  MetadataDatabase* metadata_database =
+      sync_engine()->GetMetadataDatabaseForTesting();
   GURL origin = extensions::Extension::GetBaseURLFromExtensionId(kAppID);
 
   sync_engine()->RegisterOrigin(origin, CreateResultReceiver(&sync_status));
@@ -214,7 +215,8 @@ TEST_F(SyncEngineTest, UpdateRegisteredApps) {
     EXPECT_EQ(SYNC_STATUS_OK, sync_status);
   }
 
-  MetadataDatabase* metadata_database = sync_engine()->GetMetadataDatabase();
+  MetadataDatabase* metadata_database =
+      sync_engine()->GetMetadataDatabaseForTesting();
   FileTracker tracker;
 
   ASSERT_TRUE(metadata_database->FindAppRootTracker("app_0", &tracker));