chromium/src/third_party/blink/web_tests/http/tests/serviceworker/resources/mime-type-worker.php

<?php
if ($_GET['mime']) {
  header("Content-Type: " . $_GET['mime']);
} else {
  // Set a header and remove it to override the default 'text/html'.
  header("Content-Type:");
  header_remove("Content-Type");
}
?>