Examine source code of Print The Pages

{
  "name": "Print The Pages",
  "version": "2.2",
  "description": "Sends print job directly to the printers installed on the Chromebook",
  "permissions": [
    "printing"
  ],
  "browser_action": {
    "default_popup": "printers.html",
    "default_icon": "icons/icon.png"
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "{d40c8a50-21fb-4904-a165-2a4f5f4c0df3}"
    }
  }
}