Examine source code of Google Chat Notification

{
  "browser_action": {
    "browser_style": true,
    "default_title": "__MSG_extName__",
    "default_icon": {
      "20": "icons/googlechat19.png",
      "40": "icons/googlechat38.png"
    },
    "default_popup": "popup.html"
  },
  "icons": {
    "50": "icons/googlechat.png",
    "100": "icons/googlechat@2x.png"
  },
  "description": "__MSG_extDesc__",
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "permissions": [
    "alarms",
    "https://chat.google.com/*",
    "https://mail.google.com/*",
    "notifications",
    "storage",
    "tabs"
  ],
  "manifest_version": 2,
  "name": "Google Chat Notification",
  "version": "1.5.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "google-chat-notification@euhe.in",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  },
  "default_locale": "en",
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "content_scripts": [
    {
      "matches": [
        "https://chat.google.com/*",
        "https://mail.google.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ]
}