[SyncFS] Fix leak on MetadataDatabase

chrome/browser/sync_file_system/drive_backend/metadata_database.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/metadata_database.h"
 
 #include <stack>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 623 matching lines @@
     scoped_ptr<FileMetadata> file(
         CreateFileMetadataFromChangeResource(change));
     std::string file_id = file->file_id();
 
     MarkTrackersDirtyByFileID(file_id, batch.get());
     if (!file->details().deleted())
       MaybeAddTrackersForNewFile(*file, batch.get());
 
     if (FindTrackersByFileID(file_id, NULL)) {
       PutFileToBatch(*file, batch.get());
-      file_by_id_[file_id] = file.release();
+
+      FileMetadata* file_ptr = file.release();
+      std::swap(file_ptr, file_by_id_[file_id]);
+      delete file_ptr;
     }
   }
 
   WriteToDatabase(batch.Pass(), callback);
 }
 
 MetadataDatabase::MetadataDatabase(base::SequencedTaskRunner* task_runner)
     : task_runner_(task_runner), weak_ptr_factory_(this) {
   DCHECK(task_runner);
 }
@@ skipping 369 matching lines @@
       FROM_HERE,
       base::Bind(&leveldb::DB::Write,
                  base::Unretained(db_.get()),
                  leveldb::WriteOptions(),
                  base::Owned(batch.release())),
       base::Bind(&AdaptLevelDBStatusToSyncStatusCode, callback));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system