Examine source code of sayHola

{
  "manifest_version": 2,
  "name": "__MSG_extName__",
  "homepage_url": "http://sayhola.io/",
  "description": "__MSG_extDescription__",
  "default_locale": "en",
  "permissions": [],
  "icons": {
    "16": "icons/16.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "__MSG_extName__",
    "default_icon": {
      "19": "icons/19.png",
      "38": "icons/38.png"
    }
  },
  "version": "0.2.1",
  "content_security_policy": "script-src 'self' ; object-src 'self'"
}