Construct the DatabaseFileUsageBackend.
Drupal\Core\Database\Connection $connection: The database connection which will be used to store the file usage information.
string $table: (optional) The table to store file usage info. Defaults to 'file_usage'.
public function __construct(Connection $connection, $table = 'file_usage') {
$this->connection = $connection;
$this->tableName = $table;
}