Draft answer

Use the `onCompleted` event with a filter for `xmlhttprequest`. This method will run **when the request has finished**. It's possible that the page has not been rendered yet.

 

    // In background.js:

    chrome.webRequest.onCompleted.addListener(function(details) {

        chrome.tabs.executeScript(details.tabId, {

            file: 'contentscript.js',

            allFrames: true // <-- You might want to tweak this

        });

    }, {

        urls: ['http://example.com/foo.js*'],

        types: ['xmlhttprequest']

    });

 

[`chrome.tabs.executeScript`][1] will execute the content script when the page has loaded.

 

 

  [1]: http://code.google.com/chrome/extensions/tabs.html#method-executeScript