Get current tab selection HTML

You can access to html content with chrome.tabs.executeScript . See http://code.google.com/chrome/extensions/tabs.html

I have once written a user JavaScript for Opera inspired by the "view selection source" functionality from Mozila/Firefox. You can read about it and grab the code here.

Edit: Now when I read the question you linked I realized that I actually also wrote the first Chrome extension mentioned in the answer. It was also based on that script. However, it stopped working with some Chrome update and I never look into that issue. Nevertheless, it should be pretty easy to fix.