An attacker can build a hidden form that submits to a URL at the victim site, and submit it repeatedly using javascript. Alternatively an attacker could put the test content in the URL (we don't care if it 404s), which would work just as well and allow them to use a series of script-free pages full of images.

edit: tptacek is absolutely right; there isn't a way to defend against this in application code. All you can do is turn off TLS compression. This is NOT by any means the only approach, it's just the most obvious one.