REGRESSION (r112217): H&R Block tax site won't load

REGRESSION (r112217): H&R Block tax site won't load
https://bugs.webkit.org/show_bug.cgi?id=82964

Source/WebCore:

Modifies the redirect checking code to first check if the security origin can
request the redirect URL before invoking the CORS check.

Reviewed by Adam Barth.

http/tests/xmlhttprequest/access-control-and-redirects-async.html

* loader/DocumentThreadableLoader.cpp:
* loader/DocumentThreadableLoader.h:

LayoutTests:

Add a test case for a same origin request with a custom header that receives a
same origin redirect, and therefore should pass the redirect check.

Reviewed by Adam Barth.

* http/tests/xmlhttprequest/access-control-and-redirects-async-expected.txt:
* http/tests/xmlhttprequest/access-control-and-redirects-async.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@112997 268f45cc-cd09-0410-ab3c-d52691b4dbfc