[c3RlcGhlbnI_]

There is always the option of not messing with the request at all. Instead actually have it redirect through google. For example you could have the background script do:

  chrome.browserAction.onClicked.addListener(function(tab) {
    chrome.tabs.executeScript({
      code: 'window.stop(); window.location = "http://www.google.com/badurl/' + encodeURIComponent(tab.url) + '";' 
    });
  });

and then you can have a content script run on "http://www.google.com/badurl/*" which just does:

  window.location = decodeURIComponent(window.location.pathname.split("/")[2]);

Now that is super brittle compared to your solution, but it does work(for the sites I tried, some may require you to actually fake a search query). It only requires the activeTab permission and content script permissions on one page.