I supposed that every request will invoke onBeforeRequest, but it seems not. Below is an example from google doc, and I insert console.log to see if any request invoke onBeforeRequest.
chrome.webRequest.onBeforeRequest.addListener(
function(details) {
console.log(details.url);
return {cancel: details.url.indexOf("://www.evil.com/") != -1};
},
{urls: ["<all_urls>"]},
["blocking"]);
Some websites, for example, Facebook, will not print anything on the console.
What kind of requests will be captured by onBeforeRequest?