Revert "Issue #3040166 by willzyx, Mile23, alexpott, cilefen: mkdir() fails in...

Revert "Issue #3040166 by willzyx, Mile23, alexpott, cilefen: mkdir() fails in BrowserHtmlDebugTrait.php:141 because of a race condition"

This reverts commit c080fb87.

core/tests/Drupal/Tests/BrowserHtmlDebugTrait.php

@@ -137,8 +137,8 @@ protected function initBrowserOutputFile() {
       $this->htmlOutputDirectory = DRUPAL_ROOT . '/sites/simpletest/browser_output';
       // Do not use the file_system service so this method can be called before
       // it is available.
-      if (!is_dir($this->htmlOutputDirectory) && !mkdir($this->htmlOutputDirectory, 0775, TRUE) && !is_dir($this->htmlOutputDirectory)) {
-        throw new \RuntimeException(sprintf('Unable to create directory: %s', $this->htmlOutputDirectory));
+      if (!is_dir($this->htmlOutputDirectory)) {
+        mkdir($this->htmlOutputDirectory, 0775, TRUE);
       }
       if (!file_exists($this->htmlOutputDirectory . '/.htaccess')) {
         file_put_contents($this->htmlOutputDirectory . '/.htaccess', "<IfModule mod_expires.c>\nExpiresActive Off\n</IfModule>\n");