chromium/third_party/blink/web_tests/external/wpt/service-workers/service-worker/resources/fetch-request-no-freshness-headers-script.py

def main(request, response):
    headers = []
    # Sets an ETag header to check the cache revalidation behavior.
    headers.append((b"ETag", b"abc123"))
    headers.append((b"Content-Type", b"text/javascript"))
    return headers, b"/* empty script */"