Chrome Version       : 57.0.2946.0 Revision 883e7b724370402ca8709a69ccec538e04f0bc2b-refs/heads/master@{#437239}
URLs : https://github.com/w3c/web-platform-tests/blob/master/fetch/api/cors/cors-preflight.html http://web-platform.test:8000/fetch/api/cors/cors-preflight.html
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari: OK (WebKit Nightly)
    Firefox: OK
         IE: Fail [no fetch() support]

What steps will reproduce the problem?
(1) Run https://github.com/w3c/web-platform-tests/blob/master/fetch/api/cors/cors-preflight.html in a browser (e.g., from http://web-platform.test:8000/fetch/api/cors/cors-preflight.html, if you have a local web-platform-tests environment set up)
(2) Notice failures for “assert_equals: Access-Control-Allow-Headers value expected … but got …”

What is the expected result?
Expected no failures.


What happens instead?
Got failures for “assert_equals: Access-Control-Allow-Headers value expected … but got …”

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

The failures are because the expected result is a list of header names separated only be "," (comma), but Blink instead returns a list of header names separate by ", " (comma+space).