DocumentThreadableLoader::getShouldUseCredentialStorage should allow for synchronous callbacks from SubresourceLoader::create.
https://bugs.webkit.org/show_bug.cgi?id=28728

Patch by David Levin <levin@chromium.org> on 2009-08-25
Reviewed by Maciej Stachowiak.

Test: This code path is exercised while running xhr layout tests in chromium.

* loader/DocumentThreadableLoader.cpp:
(WebCore::DocumentThreadableLoader::getShouldUseCredentialStorage): When called
back synchronously, the loader is 0, so the assert is changed to allow for that.
(WebCore::DocumentThreadableLoader::loadRequest): Synchronous callbacks may be
done before SubresourceLoader::create finishes, so ensure that any previous loader
-- from a preflight request -- is cleared before calling SubresourceLoader::create.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@47770 268f45cc-cd09-0410-ab3c-d52691b4dbfc