gaggle_output.html allows user to open a list of genes in multiple webhandlers as iframes. This creates a much better view for users to investigate multiple sites at once.

We need to pass data from the gaggle_output.html to iframes. This is accomplished by exchanging data between the Chrome Goose background page and the content scripts injected to iframes. See manifest.json for settings that allow content scripts to be injected to iframes.