Examine source code of Service Worker Detector

{
  "manifest_version": 2,
  "name": "Service Worker Detector",
  "short_name": "SW Detector",
  "description": "This extension detects if a website registers a Service Worker.",
  "author": "Thomas Steiner (tomac@google.com, @tomayac)",
  "version": "2.4.0",
  "icons": {
    "16": "assets/icon-female.png",
    "48": "assets/icon-female.png",
    "128": "assets/icon-female.png"
  },
  "page_action": {
    "default_icon": {
      "19": "assets/icon.png",
      "38": "assets/icon.png",
      "40": "assets/icon.png",
      "160": "assets/icon.png"
    },
    "default_popup": "popup.html",
    "default_title": "❌👷‍ No active Service Worker found."
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "contentscript.js"
      ],
      "run_at": "document_idle",
      "all_frames": false
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "minimum_chrome_version": "40"
}