chromium/third_party/blink/web_tests/external/wpt/html/links/manifest/wrong-mime-type-text-plain-manual.html

<!DOCTYPE html>
<title>Test JSON MIME Type support (text/plain)</title>
<link rel="help" href="https://html.spec.whatwg.org/#link-type-manifest" />
<link rel="manifest" href="wrong-mime-type-text-plain.webmanifest.webmanifest" />
<h1>Test JSON MIME Type support for web manifest</h1>
<p>
  To pass, the use agent must treat the manifest as not present. The response's
  Content-Type metadata "text/plain" is <strong>NOT</strong> a JSON MIME type.
</p>