Examine source code of GmailSwapChecks

{
  "manifest_version": 2,
  "name": "__MSG_extensionName__",
  "version": "2.1",
  "description": "__MSG_extensionDesc__",
  "default_locale": "en",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/mail/*"
      ],
      "js": [
        "inpage.js"
      ]
    }
  ]
}