Offline pages are being saved by a variety of methods, and some of these methods may cause a page to be generated more than once for a given online URL.  Example:

* A user navigates to test.net and a page is automatically saved.
* User then bookmarks test.net, causing another page to be saved.

The offline pages feature needs to choose which variant to render when the page is requested.

V1: We will render the most recently created offline copy of a given URL.