chromium/src/third_party/blink/web_tests/external/wpt/resource-timing/resources/preflight.py

def main(request, response):
    response.headers.set(b"Access-Control-Allow-Origin", b"*");
    response.headers.set(b"Access-Control-Max-Age", b"0");
    response.headers.set(b"Timing-Allow-Origin", b"*");
    # If this script is accessed with the header X-Require-Preflight then the
    # browser will send a preflight request. Otherwise it won't.
    if request.method == u'OPTIONS':
        response.headers.set(b"Access-Control-Allow-Headers", b"X-Require-Preflight");