1. A method comprising: scanning a response to a first HTTP request for a web page in order to identify a web object for prefetching; prefetching, from a content server, the web object prior to a browser requesting the web object; observing a plurality of child HTTP requests that are associated with the response to the first HTTP request for the web page; determining a measure of success of the prefetching, wherein the measure of success is based on whether the web object was prefetched and whether the web object was later requested by the browser; and modifying, based on the measure of success, a success rate for the web object as associated with the web page; wherein determining the measure of success comprises, after a duration of time during which an indication is not received that the web object was later requested, generating an inference that the web object was not requested by the browser, and wherein modifying the success rate is based on the inference.