how to make a chrome extension code example

Example: download chrome extension separately and then add to chrome

Fast-forward 3 years, and now Google Chrome offers chrome.downloads API (since 
Chrome 31).

After declaring "downloads" permission in the manifest, one can initiate a 
download with this call:

chrome.downloads.download({
  url: "http://your.url/to/download",
  filename: "suggested/filename/with/relative.path" // Optional
});