Allow XMLHttpRequest withCredentials to be set prior to a call to open()

https://bugs.webkit.org/show_bug.cgi?id=75194

Source/WebCore:

XMLHttpRequest.withCredentials attribute should be modifiable prior to the OPENED state per
the W3C spec. See http://dvcs.w3.org/hg/xhr/raw-file/tip/Overview.html#the-withcredentials-attribute

Reviewed by Alexey Proskuryakov.

Test: fast/xmlhttprequest/xmlhttprequest-withcredentials-before-open.html

* xml/XMLHttpRequest.cpp:
(WebCore::XMLHttpRequest::setWithCredentials):
Prevent setting the value only after the OPENED state.

LayoutTests:

Reviewed by Alexey Proskuryakov.

* fast/xmlhttprequest/xmlhttprequest-withcredentials-before-open-expected.txt: Added.
* fast/xmlhttprequest/xmlhttprequest-withcredentials-before-open.html: Added.
Validate that XMLHttpRequest.withCredentials can be set prior to a call to open().

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@103661 268f45cc-cd09-0410-ab3c-d52691b4dbfc