[SyncFS] Check MetadataDatabase availability before database operation

chrome/browser/sync_file_system/drive_backend/sync_engine.cc

 // Copyright 2013 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_engine.h"
 
 #include "base/bind.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 #include "chrome/browser/drive/drive_api_service.h"
@@ skipping 272 matching lines @@
 
 void SyncEngine::DownloadRemoteVersion(
     const fileapi::FileSystemURL& url,
     const std::string& version_id,
     const DownloadVersionCallback& callback) {
   // TODO(tzik): Implement this before we support manual conflict resolution.
   callback.Run(SYNC_STATUS_FAILED, webkit_blob::ScopedFile());
 }
 
 void SyncEngine::PromoteDemotedChanges() {
-  metadata_database_->PromoteLowerPriorityTrackersToNormal();
+  if (metadata_database_)
+    metadata_database_->PromoteLowerPriorityTrackersToNormal();
 }
 
 void SyncEngine::ApplyLocalChange(
     const FileChange& local_change,
     const base::FilePath& local_path,
     const SyncFileMetadata& local_metadata,
     const fileapi::FileSystemURL& url,
     const SyncStatusCallback& callback) {
   LocalToRemoteSyncer* syncer = new LocalToRemoteSyncer(
       this, local_metadata, local_change, local_path, url);
@@ skipping 117 matching lines @@
       should_check_remote_change_(true),
       listing_remote_changes_(false),
       sync_enabled_(false),
       conflict_resolution_policy_(CONFLICT_RESOLUTION_POLICY_LAST_WRITE_WIN),
       network_available_(false),
       weak_ptr_factory_(this) {
 }
 
 void SyncEngine::DoDisableApp(const std::string& app_id,
                               const SyncStatusCallback& callback) {
-  metadata_database_->DisableApp(app_id, callback);
+  if (metadata_database_)
+    metadata_database_->DisableApp(app_id, callback);
+  else
+    callback.Run(SYNC_STATUS_OK);
 }
 
 void SyncEngine::DoEnableApp(const std::string& app_id,
                              const SyncStatusCallback& callback) {
-  metadata_database_->EnableApp(app_id, callback);
+  if (metadata_database_)
+    metadata_database_->EnableApp(app_id, callback);
+  else
+    callback.Run(SYNC_STATUS_OK);
 }
 
 void SyncEngine::PostInitializeTask() {
   DCHECK(!metadata_database_);
 
   // This initializer task may not run if metadata_database_ is already
   // initialized when it runs.
   SyncEngineInitializer* initializer =
       new SyncEngineInitializer(this,
                                 task_runner_.get(),
@@ skipping 252 matching lines @@
         tracker.tracker_kind() == TRACKER_KIND_APP_ROOT;
     if (is_app_enabled && !is_app_root_tracker_enabled)
       EnableOrigin(origin, base::Bind(&EmptyStatusCallback));
     else if (!is_app_enabled && is_app_root_tracker_enabled)
       DisableOrigin(origin, base::Bind(&EmptyStatusCallback));
   }
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system