[SyncFS] Fix leak on MetadataDatabase

chrome/browser/sync_file_system/drive_backend/metadata_database.cc

Index: chrome/browser/sync_file_system/drive_backend/metadata_database.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/metadata_database.cc b/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
index 409f70a6f4126b749c5fc79c9f8d4aae21a3b4da..a7e08bc038f8ea42a25f62241ab5ee8589dc2d12 100644
--- a/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
+++ b/chrome/browser/sync_file_system/drive_backend/metadata_database.cc
@@ -641,7 +641,10 @@ void MetadataDatabase::UpdateByChangeList(
 
     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;
     }
   }