Examine source code of Date Calculator

{
  "manifest_version": 2,
  "name": "Date Calculator",
  "version": "0.9",
  "description": "A date calculator that shows how many days are left between any two given dates",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "browser_action": {
    "default_icon": "icons/icon-32.png",
    "default_title": "Date Calculator",
    "default_popup": "popup/popup.html"
  },
  "permissions": [
    "storage"
  ]
}