HistoryItem not updated properly when a form submission begins before a

HistoryItem not updated properly when a form submission begins before a
previous form submission has finished.
https://bugs.webkit.org/show_bug.cgi?id=76686

Reviewed by Nate Chapin.

Source/WebCore:

Test: LayoutTests/fast/loader/form-submission-before-load-{get,post}.html

* loader/FrameLoader.cpp:
(WebCore::FrameLoader::loadPostRequest):

LayoutTests:

* fast/loader/form-submission-before-load-get-expected.txt: Added.
* fast/loader/form-submission-before-load-get.html: Added.
* fast/loader/form-submission-before-load-post-expected.txt: Added.
* fast/loader/form-submission-before-load-post.html: Added.
* fast/loader/resources/form-submission-before-load-page2.html: Added.
* fast/loader/resources/form-submission-before-load-page3.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@112924 268f45cc-cd09-0410-ab3c-d52691b4dbfc