Merge 93188 - REGRESSION (r89086): All worker xhr requests trigger preflight requests.

Merge 93188 - REGRESSION (r89086): All worker xhr requests trigger preflight requests.
https://bugs.webkit.org/show_bug.cgi?id=66340

Reviewed by Adam Barth.

Test coming in a more comprehensive patch shortly. This is just a very targetted
patch to allow for easier merging.

* loader/CrossOriginAccessControl.cpp:
(WebCore::isOnAccessControlSimpleRequestHeaderWhitelist): Add referer to the list
of whitelisted headers. It can't be set by xhr so it is ok to whitelist it, but it is
set before calling this function. This is similar to what is done for "origin" in here.

TBR=levin@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=93192