Check out The Great Suspender [1] - not quite what you mean, but it basically unloads the tab and replaces it with a bare bones placeholder after it's been inactive for a bit. When you come back to it, you just click the link and it reloads the url that it had. Super handy if you're in the habit of leaving a few windows with a few dozen tabs each laying around, as I do.
I suspect the development is now suspended (heh) in favor of The Great Discarder [1], which uses Chrome's new "discard" api's for improved performance.
[1]: https://chrome.google.com/webstore/detail/the-great-suspende...