Examine source code of Gmail Auto BCC

{
  "name": "Gmail Auto BCC",
  "author": "Clockk.com Inc.",
  "homepage_url": "https://clockk.com/",
  "short_name": "Gmail Auto BCC",
  "description": "Automatically BCC all Gmail emails to list of addresses of your choosing.",
  "version": "1.0.7",
  "manifest_version": 2,
  "icons": {
    "48": "icons/clockk auto bcc 48.png",
    "128": "icons/clockk auto bcc 128.png"
  },
  "browser_action": {
    "default_title": "clockk-auto-bcc",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "page": "options/options.html",
    "chrome_style": true
  },
  "content_scripts": [
    {
      "matches": [
        "https://mail.google.com/*"
      ],
      "js": [
        "gmail.js"
      ],
      "run_at": "document_end"
    }
  ],
  "web_accessible_resources": [
    "gmail.js"
  ],
  "permissions": [
    "https://mail.google.com/*",
    "storage"
  ]
}