Is there a way to automatically generate waterfall type images for web page loading? An example is this one from Google Page Speed:

http://code.google.com/speed/page-speed/images/activity2.png

If you know of a way to generate automatically this kind of stats but not this exact type of visualization, I'm also interested.

By "automatically" I mean running scripts/programs on a server that retrieve a URL specified via some control mechanism. If it's all command line, even better.

Thanks!