HTTP Auth does not work on Chrome

like :
http://www.webpagetest.org/result/130218_DK_3939adde356201d0a9660fb458653a71/

the same page with the same HTTP authentification informations does work on IE 8.

Both in WPT.org and on my private instance

Opened an issue to track it: http://code.google.com/p/webpagetest/issues/detail?id=142

In the meantime, you should be able to use addHeader to specify a basic auth header (that’s all the IE code does internally).