Referer should be set for XMLHttpRequest from Workers.

FAIL: Sync. Expected referer: 'http://127.0.0.1:8000/xmlhttprequest/workers/resources/referer.js' Actual referer: 'http://127.0.0.1:8000/xmlhttprequest/workers/referer.html'
FAIL: Async. Expected referer: 'http://127.0.0.1:8000/xmlhttprequest/workers/resources/referer.js' Actual referer: 'http://127.0.0.1:8000/xmlhttprequest/workers/referer.html'
