https://developer.chrome.com/extensions/devtools has great overview of communicating between the various pieces, but it's still a little incomplete.

One tricky area is passing messages from a contentscript back into a devtools panel.

There's no direct connectivity between the page being inspected and DevTools extension panels -- we usually recommend this flow: DOM messaging from the injected inspected page code to the content script, then extension messaging to send that to the background page and the front-end iframe.

Example: polymer extension message passing via CustomEvent on the window

• https://github.com/PolymerLabs/polymer-devtools-extension/blob/b37837529453a487d0cc6058ac4713686157013f/hostPageHelpers.js#L786-L790
• https://github.com/PolymerLabs/polymer-devtools-extension/blob/b37837529453a487d0cc6058ac4713686157013f/contentScript.js#L7-L16

another option is: buffering events in inspected page and polling them

• Buffering events in the inspected page and then polling from the front-end by using chrome.devtools.inspectedPage.eval().
• web tracing framework does this
  • https://github.com/google/tracing-framework/blob/23abca44559b5b01f55205180e15dd019ef13204/extensions/wtf-injector-chrome/injectedtab.js#L98-L117