Add suggestion to use "no-cors" with Fetch fails CORS check.

LayoutTests/http/tests/xmlhttprequest/origin-exact-matching/35-expected.txt

 CONSOLE WARNING: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check http://xhr.spec.whatwg.org/.
-CONSOLE ERROR: XMLHttpRequest cannot load http://127.0.0.1:8000/xmlhttprequest/resources/access-control-allow-lists.php?origin=*%2C%20http%3A%2F%2Flocalhost%3A8000. The 'Access-Control-Allow-Origin' header contains multiple values '*, http://localhost:8000', but only one is allowed. Origin 'http://localhost:8000' is therefore not allowed access.
+CONSOLE ERROR: XMLHttpRequest cannot load http://127.0.0.1:8000/xmlhttprequest/resources/access-control-allow-lists.php?origin=*%2C%20http%3A%2F%2Flocalhost%3A8000. The 'Access-Control-Allow-Origin' header contains multiple values '*, http://localhost:8000', but only one is allowed. Origin 'http://localhost:8000' is therefore not allowed access. Either change the header, or, if you want an opaque response, use the Fetch API in 'no-cors' mode.
 
 
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 Frame: '<!--framePath //<!--frame0-->-->'
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 Check that exact matching is used when comparing a request's originating url and the value provided by Access-Control-Allow-Origin.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 Should disallow origin: '*, http://localhost:8000'
 PASS xhr.send(null) threw exception NetworkError: Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'http://127.0.0.1:8000/xmlhttprequest/resources/access-control-allow-lists.php?origin=*%2C%20http%3A%2F%2Flocalhost%3A8000'..
 PASS successfullyParsed is true
 
 TEST COMPLETE