[K0nserv]

I had a quick look at the 1Password chrome extension source and it seems to me like they are using window.URL[0].

See this pastebin[1] for the function I believe is determining the url of the active tab and if it has a valid hostname.

There's also this one[2] that seems to be extracting the hostname of a given url also using the URL API.

Both these pastebins contain minimized code that I've cleaned up.

0: https://developer.mozilla.org/en-US/docs/Web/API/URL

1: http://pastebin.com/tWns7XmG

2: http://pastebin.com/PXS1iqsq