Examine source code of close current window

{
  "description": "close current window. Useful for navigating without navbar",
  "manifest_version": 2,
  "name": "close button",
  "version": "1.0",
  "background": {
    "scripts": [
      "closebutton.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/close.png",
      "32": "icons/close.png"
    }
  }
}