tedster - 6:38 am on Jun 21, 2011 (gmt 0)
There are some features for developers in the works, but they don't sound very simple or easy, at least not yet. And they are not standardized, either. From the Chromium blog:
The page visibility API [w3.org] - which is in the early stages of standardization in the webperf working group - can help developers understand the visibility status of their page: whether it's in a foreground tab, a background tab, or being prerendered. This is still an experimental implementation and it may change or even be removed in the future, which is why for the time being we've prefixed the property names with "webkit." Although the page visibility API is useful for detecting prerendering, it also has many other applications--for example, allowing a site to pause expensive physics calculations when the page isn't visible.
To learn more about the page visibility API and prerendering, check out the Using the Page Visibility API [code.google.com] and Web Developers' Guide to Prerendering in Chrome [code.google.com] articles.
Pre-rendering in Chrome [blog.chromium.org]
I added the bold red style for emphasis.