How do I refresh/reload a Chrome Extension?

Now the simplest way to make extension to reload itself is to call chrome.runtime.reload(). This feature doesn't need any permissions in manifest. To reload another extension use chrome.management.setEnabled(). It requires "permissions": [ "management" ] in manifest.

The chrome.send function is not accessible by your extension's javascript code, pages like the newtab page, history and the extensions page use it to communicate with the C++ controller code for those pages.

You can push updates of your extension to users who have it installed, this is described here. The user's application will be updated once the autoupdate interval is hit or when they restart the browser. You cannot however reload a user's extension programmatically. I think that would be a security risk.