CONSOLE MESSAGE: line 35: Origin http://127.0.0.1:8000 is not allowed by Access-Control-Allow-Origin.
CONSOLE MESSAGE: line 35: XMLHttpRequest cannot load http://localhost:8000/xmlhttprequest/xmlhttprequest-sync-vs-async-assertion-failure.html due to access control checks.
Test for:

bug 40996: Progress event should not be fired during synchronous XMLHttpRequest;
bug 17502: Assertion failure when trying to restart a sync XMLHttpRequest as an async one from onreadystatechange.
 Step 1: Same origin request
readystatechange 4
load
loadend

Step 2: Cross origin request, disallowed
readystatechange 4
error
loadend
NetworkError:  A network error occurred.

Step 3: Cross origin request, allowed
readystatechange 4
load
loadend

Step 4: Cross origin request, check that preflight isn't attempted
readystatechange 4
load
loadend