Manifest:
{
  "name": "Web req test",
  "description": "Blocks Facebook requests (including cdn)",
  "version": "1.0",
  "manifest_version": 2,
  "background": {"scripts":["bg.js"]},
  "permissions": ["webRequest","webRequestBlocking","*://*.facebook.com/*", "*://*.facebook.net/*", "*://*.fbcdn.net/*", "*://fbcdn.net/*", "<all_urls>"]
}

Background script:
chrome.webRequest.onBeforeRequest.addListener(
  function(details) {
      console.log(details.method + ' ' + details.url + '   (' + details.type + ')');
      return {cancel:true};
  },
  {
    urls: [
         "<all_urls>" // Quick test
    ],
    types: ["main_frame", "sub_frame", "stylesheet", "script", "image", "object", "xmlhttprequest", "other"]
  },
  ["blocking"]
);