private function getAssetFromStream($filename, \Twig_TokenStream $stream)
{
$this->expect($filename, $stream->next(), \Twig_Token::PUNCTUATION_TYPE, '(');
$token = $stream->next();
$this->expect($filename, $token, \Twig_Token::STRING_TYPE);
$this->expect($filename, $stream->next(), \Twig_Token::PUNCTUATION_TYPE, ')');
return $token->getValue();
}