Event for failed loading of JavaScript file, XmlHttpRequest?

[HarmlessDave]

What handler(s) and event(s) should I be overriding to be able to track that a page failed to load one of its script files, or that an XmlHttpRequest timed out? I want to do this in C++ not by trying to inject code into a page.

For now I just want to log this so that when users see incomplete or incorrect pages we can tell why it's happening.