Examine source code of Tel Link Handler

{
  "manifest_version": 2,
  "name": "Tel Link Handler",
  "version": "1.0",
  "description": "Redireciona links do tipo 'tel' para o Google Contacts ou WhatsApp.",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "*://*/*",
    "storage"
  ],
  "options_ui": {
    "page": "options.html"
  },
  "protocol_handlers": [
    {
      "protocol": "tel",
      "name": "Add to Google Contacts",
      "uriTemplate": "https://contacts.google.com/new?phone=%s&source=google-contacts-from-link"
    },
    {
      "protocol": "tel",
      "name": "Send a message through WhatsApp",
      "uriTemplate": "https://web.whatsapp.com/send?phone=%s&source=google-contacts-from-link"
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "tellinkhandler@marcelothebuilder.github.com",
      "strict_min_version": "42.0"
    }
  }
}