Examine source code of Dev Headers

{
  "name": "Dev Headers",
  "short_name": "Dev Headers",
  "version": "1.0.2",
  "manifest_version": 2,
  "description": "Adds a header for dev websites.",
  "icons": {
    "16": "icons/000000/16.png",
    "48": "icons/000000/48.png",
    "128": "icons/000000/128.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/BBBBBB/16.png",
      "24": "icons/BBBBBB/24.png",
      "32": "icons/BBBBBB/32.png"
    },
    "default_title": "Dev Headers",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "content_security_policy": "default-src 'none'; base-uri 'none'; form-action 'none'; style-src 'self'; script-src 'self'; connect-src *; block-all-mixed-content"
}