Inject javascript in an iframe using chrome extension

Yes, you can use content_scripts property in manifest.json like this:

"content_scripts": [{
    "matches": ["http://*/*", "https://*/*"],
    "js": ["content_frame.js"],
    "all_frames": true
}],

By setting all_frames to true you will inject/include content_frame.js javascript file into top document and all iframes. In case you just need javascript injected in iframe but not in top document you can check inside your content_frame.js file like this:

if (parent === top) {
    // here you can put your code that will run only inside iframe
}