Examine source code of YouTubeRealTime

{
  "manifest_version": 2,
  "name": "YouTubeRealTime",
  "description": "Show remaining time regarding playback speed. ",
  "version": "0.0.1",
  "icons": {
    "64": "icons/icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/watch*"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ]
}