[SyncFS] Make routines using metadata database async

chrome/browser/sync_file_system/drive_backend/sync_worker.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/sync_file_system/drive_backend/sync_worker.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 227 matching lines @@
 void SyncWorker::SetSyncEnabled(bool enabled) {
   if (sync_enabled_ == enabled)
     return;
 
   RemoteServiceState old_state = GetCurrentState();
   sync_enabled_ = enabled;
   if (old_state == GetCurrentState())
     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_,
+        OnPromoteDemotedChanges(metadata_db->CountDirtyTracker()));
+  }
+}
+
 SyncStatusCode SyncWorker::SetDefaultConflictResolutionPolicy(
     ConflictResolutionPolicy policy) {
   default_conflict_resolution_policy_ = policy;
   return SYNC_STATUS_OK;
 }
 
 SyncStatusCode SyncWorker::SetConflictResolutionPolicy(
     const GURL& origin,
     ConflictResolutionPolicy policy) {
   NOTIMPLEMENTED();
@@ skipping 430 matching lines @@
             "Service state changed: %d->%d: %s",
             old_state, GetCurrentState(), description.c_str());
 
   FOR_EACH_OBSERVER(
       Observer, observers_,
       UpdateServiceState(GetCurrentState(), description));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system