title: Send message to content script that lives outside of a tab?
body: <p>Here's my setup; I have my browser action pull up popup.html which runs my main script. I also have a background.html running in the background which in it has an iframe. I have a content script that runs in the page I pull into the iframe. Picture for clarity:</p>
  
  <p><img src="https://i.stack.imgur.com/hPMfL.png" alt="enter image description here"></p>
  
  <p>I need to be able to send a message from main_script.js to content_script.js. This is usually done with something like chrome.tabs.sendMessage which requires a tab id along with every other method I've found for message passing TO a content script FROM a script elsewhere. The thing is, with this setup, my content script doesn't have a tab id for me to use to send it a message.</p>
  
  <p>Is there some other way to do this that I'm not aware of?</p>