[SyncFS] Make routines using metadata database async

chrome/browser/sync_file_system/drive_backend/sync_worker.cc

Index: chrome/browser/sync_file_system/drive_backend/sync_worker.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/sync_worker.cc b/chrome/browser/sync_file_system/drive_backend/sync_worker.cc
index 1d99ebea6cab006ff2d219c3a82cef31cbcf685e..884198940690157003b4fb00b99e3db75dec4842 100644
--- a/chrome/browser/sync_file_system/drive_backend/sync_worker.cc
+++ b/chrome/browser/sync_file_system/drive_backend/sync_worker.cc
@@ -245,12 +245,24 @@ void SyncWorker::SetSyncEnabled(bool enabled) {
     return;
 
   FOR_EACH_OBSERVER(
-      Observer, observers_,
+      Observer,
+      observers_,
       UpdateServiceState(
           GetCurrentState(),
           enabled ? "Sync is enabled" : "Sync is disabled"));
 }
 
+void SyncWorker::PromoteDemotedChanges() {
+  MetadataDatabase* metadata_db = GetMetadataDatabase();
+  if (metadata_db && metadata_db->HasLowPriorityDirtyTracker()) {
+    metadata_db->PromoteLowerPriorityTrackersToNormal();
+    FOR_EACH_OBSERVER(
+        Observer,
+        observers_,
+        OnPendingFileListUpdated(metadata_db->CountDirtyTracker()));
+  }
+}
+
 SyncStatusCode SyncWorker::SetDefaultConflictResolutionPolicy(
     ConflictResolutionPolicy policy) {
   default_conflict_resolution_policy_ = policy;