UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36

Steps to reproduce the problem:
1. create a CORS fetch request to a url that has content-length in its response and doesn't add content-length to access-control-expose-headers
2.  content-length should be accessible in the response's headers
3. 

What is the expected behavior?
When doing a CORS fetch request if content-length exists in the http response it should be exposed on the response headers even if it's not added to the access-control-expose-headers.

see:
https://github.com/whatwg/fetch/pull/626
https://github.com/w3c/web-platform-tests/pull/10930

What went wrong?
content-length is not exposed

Did this work before? N/A 

Does this work in other browsers? No

Chrome version: 66.0.3359.139  Channel: stable
OS Version: OS X 10.12.6
Flash Version: