Chrome Version       : 67.0.3396.62
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari: FAIL (No support for SharedWorker)
    Firefox: OK
    IE/Edge: FAIL (No support for SharedWorker)

What steps will reproduce the problem?
1. Clone this gist: https://gist.github.com/surma/80f5ceee14471644ff2fe1db602b32bd
2. Serve it via HTTP
3. Watch the console

What is the expected result?
A couple of log messages

What happens instead of that?
Nothing. Not even a request for the SharedWorker file.

Please provide any additional information below. Attach a screenshot if
possible.

UserAgentString: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.62 Safari/537.36