PHP Warning:  require(/var/www/piwik/vendor/facebook/xhprof/xhprof_lib/utils/xhprof_lib.php): failed to open stream: No such file or directory in /var/www/piwik/vendor/composer/autoload_real.php on line 58
PHP Fatal error:  require(): Failed opening required '/var/www/piwik/vendor/facebook/xhprof/xhprof_lib/utils/xhprof_lib.php' (include_path='/var/www/piwik/vendor/phpunit/php-text-template:/var/www/piwik/vendor/phpunit/phpunit-mock-objects:/var/www/piwik/vendor/phpunit/php-timer:/var/www/piwik/vendor/phpunit/php-file-iterator:/var/www/piwik/vendor/phpunit/php-code-coverage:/var/www/piwik/vendor/phpunit/phpunit:/var/www/piwik/vendor/symfony/yaml:.:/usr/share/php:/usr/share/pear') in /var/www/piwik/vendor/composer/autoload_real.php on line 58

In /var/www/piwik/vendor/composer/autoload_files.php need to be comented in order to fix this:
#    $vendorDir . '/facebook/xhprof/xhprof_lib/utils/xhprof_lib.php',
#    $vendorDir . '/facebook/xhprof/xhprof_lib/utils/xhprof_runs.php'