Google Chrome Extension - waiting until page loads

Question

In my Google Chrome Extension, I have a Content Script (content.js) and a Background Page (background.html). I have context.js checking for a keyword that appears on the page. However, I want to wait until the page is fully loaded until I search the page, because the keyword may occur at the bottom of the page.

See Page action by content sandwich example (files), this is basically what I am doing. If you load the extension you'll see the extension only works when the word "sandwich" appears at the top of the page.